Abstract: The structural characteristics of novel alkaline-earth suborthosilicate glasses along the compositional join (1 â x)(0.5CaO.0.5MgO) â xSiO2 with
0.28 ⤠x ⤠0.33 are investigated using high resolution 29Si and 17O nuclear magnetic resonance spectroscopy. The structures of these glasses consist of isolated Q0 and Q1 anionic species and Mg2+ and Ca2+ countercations that are held together by Coulombic interactions. The concentration of the Q1 species rapidly decreases with decreasing SiO2 content and becomes undetectable in the glass with x = 28 mol %. The compositional variation of the physical properties of these glasses such as glass transition temperature and density can be attributed to
the Q-speciation in the structure. The NBOs are associated with a random distribution of the alkaline-earth cations in their nearest neighbor coordination shell. The resulting random packing of dissimilar Ca-NBO and Mg-NBO coordination polyhedra may give rise to structural and topological frustration responsible for
the unusual glass-forming ability of these suborthosilicate liquids with extremely low SiO2 contents. Finally, the composition and the formation of Q1 species necessitate the formation of free O2â ions in the structure of these glasses that are only bonded to Mg2+ and Ca2+ cations. The 17O NMR results presented in this study allow for direct observation of such oxygen species.
Abstract: The thermal decomposition of SiC surface provides, perhaps, the most
promising method for the epitaxial growth of graphene on a material useful
in the electronics platform. Currently, efforts are focused on a reliable method
for the growth of large-area, low-strain epitaxial graphene that is still lacking.
Here, a novel method for the fast, single-step epitaxial growth of large-area
homogeneous graphene film on the surface of SiC(0001) using an infrared
CO2 laser (10.6 μm) as the heating source is reported. Apart from enabling
extreme heating and cooling rates, which can control the stacking order of
epitaxial graphene, this method is cost-effective in that it does not necessitate
SiC pre-treatment and/or high vacuum, it operates at low temperature
and proceeds in the second time scale, thus providing a green solution to EG
fabrication and a means to engineering graphene patterns on SiC by focused
laser beams. Uniform, lowâstrain graphene film is demonstrated by scanning
electron microscopy, X-ray photoelectron spectroscopy, secondary ion-mass
spectroscopy, and Raman spectroscopy. Scalability to industrial level of the
method described here appears to be realistic, in view of the high rate of CO2-
laser-induced graphene growth and the lack of strict sampleâenvironment
conditions.
Abstract: The structural attributes of the polyamorphic high- and low-density amorphous phases in Y2O3-Al2O3 glasses with 24-41 mol % Y2O3 have been investigated using
high-resolution 27Al and 89Y nuclear magnetic resonance spectroscopy in combination with back-scattered electron and transmission electron microscopy imaging and differential scanning calorimetric measurements. Glasses over the entire composition range are characterized by a uniform dispersion of droplets of one phase in the matrix of the other phase resulting from a density-driven phase separation in the supercooled liquid state. Although compositionally identical, the structures of the two phases differ primarily in their Y coordination environment and in the structural order associated with the connectivity and packing of the Al-O and Y-O coordination polyhedra. It appears that,
compared to the matrix phase, the droplet phase is characterized by a significantly higher degree of short-range structural order.
Abstract: Container-less levitation techniques and CO2 laser heating were used to prepare a series of silicate glasses along the compositional join (1-x)(Ca,Mg)O-xSiO2 beyond the orthosilicate limit for the first time with the silica mole fraction x ranging
between 0.33 and 0.27. Raman spectroscopic measurements in the
temperature range 25-700 C show complete absence of connectivity
between the SiO4 tetrahedra in glasses with x < 0.3. The corresponding glass structures are characterized by isolated negatively charged âtetrahedralâ SiO4
4- and O2- anions with M2+ (M = Mg,Ca) as the counter cations, held together by pure Coulombic (ionic) interactions. This structural view is supported by semiempirical
MO simulations which were used to derive the structure of the Ca,Mg suborthosilicate glass 0.5(1-x)CaO-0.5(1-x)MgO-xSiO2 with x = 0.286. The Raman spectra permit the experimental determination of all the vibrational modes of the isolated SiO44-
tetrahedra in silicate glasses.
Abstract: Ramanspectraof xTeO2â(1-x)GeO2 (x=0, 0.2,0.4,0.6,0.8and1) germaniumtellurite glasses were measured and analyzed in an effort to follow the structural changes caused by mixing two typical glass formers. Systematic Raman intensity measurements have been performed in an effort to elucidate the composition induced structural changes and a possible mechanism accounting for these changes was proposed. The network structure of the glass ischaracterized byTeO4 trigonal bipyramid mixed with
TeO3 trigonal pyramid units, while GeO4 tetrahedra lunits are also present. Changing the GeO2 content results in the conversion of the TeO4 units toTeO3 units with a neutral doubly bridged oxygen atom, while the existence of charged terminal oxygen atoms is questionable. The measured relative Raman intensities are semi-quantitatively correlated to the transformation of the TeO4 trigonal bipyramid to TeO3 trigonal pyramids.
Abstract: Six glasses in the Y2O3âAl2O3 binary system with compositions ranging between 24 and 41 mol% Y2O3 have been prepared by containerless levitation and CO2 laser melting techniques. Polarized and depolarized Raman spectra measured at
ambient conditions for all glasses have a high intensity boson peak at ~100 cmâ1 and three polarized bands at frequencies νA=780 , νB=650 and νC=450 cmâ1. The relative intensities of the νA, νB and νC bands are dependent on glass composition and are assigned to stretching of AlâO terminal bonds in Q2-AlO4 type species, AlâOâAl and YâO stretching vibrations respectively. Raman spectral measurements at temperatures of up to 1100 K do not show any significant change in the relative intensities of the νA, νB and νC bands. The boson peak is found to be independent of both composition and temperature and its frequency is used to estimate correlation lengths of structural order in these glasses. It appears that the YâO and AlâO polyhedra in the glass network are linked via AlâOâAl and AlâOâY bridges while the presence of AlâO terminal bonds offers a partial ionic character to the glass structure. Micro-Raman spectra measured for the low and high density amorphous phases formed in these glasses are found to be indistinguishable indicating common structural characteristics for both phases. It appears that the stability of the high density phase against crystallization is higher than
that of the low density phase. Finally extensive polarization measurements suggest the Raman depolarization ratio is a sensitive indicator for monitoring phase separation in glasses at micron to nanometre length scales.
Abstract: In situ quantitative Raman spectra of vitreous and molten silica were measured from LN2 temperatures up to above melting and used to calculate the intensities of the two âdefect peaksâ D1 and D2 associated with the corresponding four- and three- membered ring structures. The D1 intensity decreases with increasing temperature while the D2 intensity appears to be invariant on temperature. The data are in disparity with the quenching / fictive temperature experiments and show definitely no abrupt intensity changes at any temperature.
Abstract: A series of glasses xMgOâ(1âx)SiO2 with compositions from enstatite MgSiO3 (x=0.5) to
forsterite Mg2SiO4 (x=0.667) in mole fraction intervals of x=0.02 have been prepared by containerless levitation techniques and CO2 laser heating. Polarized and depolarized Raman spectra measured at ambient conditions for all these glasses show systematic and smooth band intensity changes with composition. Analysis of the Raman band contours in terms of vibrations due to different oxygen bridged SiO4 tetrahedra (Qi, species analysis) undoubtedly shows that bridging oxygens are present in all glasses studied even in the limit of the forsterite composition where
bridged Si2O7- ionic dimers are formed. Furthermore the relative amounts of the Qi species change smoothly with composition while at high MgO content âfreeâ oxygens are present presumably forming MgâOâMg bridges, which contribute to the glass stability at these compositions. Raman spectra measurements at different temperature below Tg show small alterations in the Qi species in the MgSiO3 region while no changes were observed in the Mg2SiO4 region. The Boson peak frequency is practically invariant on both composition and temperature and this is in contrast to the
systematics followed by most silicate glasses. It is suggested that at compositions near the forsterite ioniclike glasses are formed arising from a very fragile liquid.
Abstract: The electronic absorption spectra of the f â f transitions of Ho3+ as a probe cation doped in solid and liquid YCl3 and TbCl3 have been measured from room temperature to above the melting point of both compounds. In the same temperature range Raman spectroscopy has been utilized to characterize all phases present. Emphasis is given on the Ho3+ ligand field spectra of the 5G6 â 5I8 hypersensitive transition and their similarities with the known spectra of holmium chloro-elpasolite. Smooth spectral changes with nearly invariant molar absorptivities (between 30 and 40 L molâ1 cmâ1) are observed upon melting YCl3 and -TbCl3 which indicate that most probably the Ho3+ is in 6-fold distorted octahedral coordination in both compounds and both phases. Drastic spectral changes are observed alongside the -TbCl3 to β-TbCl3 phase transition where the coordination is altered from six to eight and the molar absorptivity quadruples. The spectra of liquid Y(Ho)Cl3 and Tb(Ho)Cl3 are correlated to the spectra of liquid La(Ho)Cl3 and Gd(Ho)Cl3 and are attributed to the ligand field states of Ho3+ in distorted octahedral geometries. In conjunction with the molar volumes of all RCl3 (R = rare earth) liquids which are invariant and independent of R and with Raman spectroscopic measurements for the same systems, a common possible structure of the rare earth chloride liquids is deduced and proposed.
Abstract: We present a detailed dynamic light scattering study of the phase separation in the ocular lens emerging
during cold cataract development. Cold cataract is a phase separation effect that proceeds via spinodal decomposition
of the lens cytoplasm with cooling. The intensity autocorrelation functions of the lens protein content
are analyzed with the aid of two methods, providing information on the populations and dynamics of the
scattering elements associated with cold cataract. It is found that the temperature dependence of many measurable
parameters changes appreciably at the characteristic temperature 161 °C which is associated with
the onset of cold cataract. By extending the temperature range of this work to previously inaccessible regimes,
i.e., well below the phase separation or coexistence curve at Tcc, we have been able to accurately determine the
temperature dependence of the collective and self-diffusion coefficients of proteins near the spinodal. The
analysis showed that the dynamics of proteins bears some resemblance to the dynamics of structural glasses,
where the apparent activation energy for particle diffusion increases below Tcc, indicating a highly cooperative
motion. Application of ideas developed for studying the critical dynamics of binary protein-solvent mixtures,
as well as the use of a modified Arrhenius equation, enabled us to estimate the spinodal temperature Tsp of the
lens nucleus. The applicability of dynamic light scattering as a noninvasive, early-diagnostic tool for ocular
diseases is also demonstrated in light of the findings of the present paper.
Abstract: Raman spectroscopy is used to characterize the NbF5 phases in the temperature range 80â500 K. A new clear glass is formed by quenching the melt to liquid nitrogen temperatures having a glass transition at ~206 K and crystallization at ~233 K. For all phases including the melt, the glass, the supercooled liquid, the crystalline solid and the gas, the Raman spectra show a rather common high frequency band at ~760 cm-1 which is attributed to the NbâF terminal frequency of partially bridged âNbF6â octahedra. Based on the systematics of the Raman spectra for all phases and the literature physicochemical data a model is proposed for the glass and the liquid phases where âNbF6â octahedral bridged in cis and/or trans configurations form a variety of cyclic and/or chain structures which intermix building up the overall structure. At exceptionally low energies (<11 cm_1) a rather weak in intensity Boson peak is observed in the glass which shifts to even lower energies with increasing temperature. Librational and/or tortional motions of the bridged octahedra participating in the glass structure are possible candidates for the origin of this peak.
Abstract: Electronic absorption and Raman spectra of solid and molten Cs2NaHoCl6 elpasolite have been measured in the temperature range 20 â 780 â¦C. The Raman spectra of the solid indicate that there is no phase transition above room temperature. It appears, that the internal vibrational modes of the solid are transferred into the melt, indicating that the [HoCl6]3â âoctahedraâ are the predominant species. The 5G6 â5I8 and 3H6 â5I8 hypersensitive transitions of Ho(III) in elpasolite have been studied and analyzed in terms of the ligand field splittings of these states in the octahedral [HoCl6]3â field. The temperature-induced changes in the spectra are attributed to the presence of âhotâ bands arising from sets (âzonesâ) of energy levels in the ground 5I8 state. The continuous and smooth spectral changes observed upon melting indicate the presence of [HoCl6]3â octahedra in both phases.
Abstract: Electronic absorption spectroscopy is used in the temperature range 850â1300 K, to study the vapor species over molten HoI3âCsI(1:1), molten CsI and solid HoI3. Quantitative absorbance measurements are used to calculate the following enthalpies of transition: Dhsubl(HoI3) = 271 ± 3 kJ /mol, Dhvap. (CsHoI4) = 155 ± 2 kJ /mol and Dhvap. (CsI) = 151 ± 2 kJ/ mol. The ligand field componentsof the 5G6 -5I8 hypersensitive transition of Ho(III) for the three different, all iodide, coordination geometries of HoI3(g), CsHoI4(g) and HoI6
3- (in molten CsI) have been examined in detail. The molar absorptivities (e) and oscillator strengths (f) increase
as the coordination decreases from the ââoctahedralââ HoI6
(e = 65 L mol1 cm1; f = 99 · 106) to the distorted tetrahedral HoI4
(e = 235 L mol1 cm1; f = 290 · 106) to the trigonal HoI3 (e = 390 L mol1 cm1; f = 500 · 106). The main factors affecting the
hypersensitive transition intensities are the coordination number and symmetry and the ligand polarizability as well as the Boltzmann
population effects on the ground state levels which are responsible for the appearance of ââhotââ bands in the spectra. A C2v symmetry
is anticipated for the CsHoI4(g) with the HoI4 ââtetrahedraââ distorted towards a square planar symmetry leading to a structure with
a pseudo-like inversion center.
Abstract: In this work, a new 514.5-nm laser light delivery probe is
developed for the in situ quantification of the concentration of
medicinal substances injected in the anterior chamber of the
eye. The probe is adapted to a commercial CCD-based Raman
spectrometer and employs a 90-deg scattering geometry to
minimize the risk of damaging the ocular tissue. Compared toearlier designs, the present setup implements a number of
modifications in the collection optics to match the scattering
volume with the entrance slit of the spectrometer and to improve
the signal-to-noise ratio. Porcine eyes fitted to an AAC are employed to simulate the eye as an optical cell, and PLS
chemometric models are developed to correlate the Raman
spectra with the concentration of the drug in the aqueous humor
of the eye.
The probe has been evaluated by determining the concentration
of ciprofloxacin, an antibiotic of the fluoroquinolone
family. The concentration of this drug can be predicted with
an RMS error of ca. 40 g/mL that compares favorably with
the suggested, target-dependent, minimum inhibitory concentrations
of this drug 0.016 to 1024 g/mL. Furthermore,
we have demonstrated that the current performance of the
method is limited by the spurious vibrational signatures of the
polymeric components of the AAC cell and therefore is expected
to improve if intact eyes are studied.
Future studies are oriented toward the combined use of
Raman spectroscopy and chemometric modeling to the early
diagnosis of intraocular diseases in vivo, as well as toward the
monitoring of pharmacokinetics of the administered drugs. It
is anticipated that beyond the management of ocular fungal
infections, this technique might be applicable to the identification
of illegal substances in the aqueous humor of the eye,
especially since several of these compounds are strong Raman
scatterers.
Abstract: The electronic absorption spectra of the f â f transitions of Ho(III) in solid and molten Cs2NaHoCl6 elpasolite and in Y(Ho)Cl3 have been measured from room temperature up to above the melting point of both compounds. Emphasis is given on the ligand field spectra of the 5G6 â 5I8 hypersensitive transition. Smooth spectra changes are observed upon melting the solids. In conjuction with Raman spectroscopic measurements the absorption spectra are attributed to HoCl octahedra in distorted geometries. The spectra of molten Y(Ho)Cl3 are correlated to the elpasolite spectra as well as with the spectra of La(Ho)Cl3 and Gd(Ho)Cl3 to deduce the possible structure of the host rare-earth chlorides.
Abstract: Raman scattering has been employed to study the temperature and composition dependence of the vibrational modes for the glassforming
oxyhalide mixtures xLiClâ(1âx)TeO2 (x ¼ 0, 0.2, 0.3, 0.35, 0.5 and 0.67) in the glassy, supercooled and liquid state up to 600 1C.
The analysis has shown that the network structure of the glass/melt is formed by mixing trigonal bipyramid and trigonal pyramid units.
The change of LiCl content and/or temperature results to conversion of the trigonal bipyramid to trigonal pyramid units with a varying
number of non-bridging chlorine and oxygen atoms. The fraction of the terminal oxygen atoms doubly bonded to tellurium versus
temperature has been directly estimated from the Raman spectroscopic results with the aid of a structural model concerning the tellurite
network systems. A well-resolved Boson peak (BP) dominates the low-frequency Raman spectra. The temperature dependence of the
maximum of the BP has also been determined and discussed in the framework of its microscopic origin.
Abstract: Raman spectra of xNa2O(1x)TeO2 glasses were measured and analyzed over a broad composition range. The network structure of
the glass consists of a mixture of TeO4 trigonal bipyramids and TeO3 trigonal pyramidal units. Increase of alkali content results in
conversion of the TeO4 units into TeO3 units with a varying number of non-bridging oxygen atoms. This local structure transformation
becomes more evident at x ¼ 0.2, where rigidity percolation theory predicts a threshold for the rigid-to-floppy transition. However, other
spectral features such as the composition dependence of the energy of the Boson peak do not support the occurrence of the stiffness
transition. The controversial dependence of dynamical parameters such as the fragility index as a function of Na2O concentration is also
discussed.
Abstract: Electronic absorption spectroscopy is used in the temperature range 800â1400 K, to study the vapor species, over molten CrCl3âACl
A = Li, Cs) mixtures and solid CrCl3. The observed Vis/near IR bands are assigned to d â¹ d transitions of Cr3+ in distorted ââtetrahedralââ
coordination ðCrCl4Ã. Spectra of ââoctahedralââ CrCl6
3 in molten alkali chlorides were also measured and used to estimate the
spectroscopic constants (Dq, B, C) of Cr3+ in all chloride tetrahedral and octahedral environments. Composition and temperature-dependent
measurements suggest that the predominant vapor species is the 1:1 monomer ACrCl4 and that an equilibrium is established:
ACrCl4 (g) = CrCl3 (g)+ACl (g)
Due to vapor complexation the apparent vapor pressure of CrCl3 increases. The volatility enhancement is higher for the LiClâCrCl3 than
the CsClâCrCl3 system reaching values near 60, at 950 K. Based on the preferential octahedral ligand field stabilization energy of
Cr(III) it is argued that dimeric and/or trimeric 1:1 species may be also present as minor components in the vapor phase. Finally, the
vapor complexation and volatility enhancement for the MX3âAX (M = rare earth, Cr; X = halide) systems are discussed and correlated
to the melt structure of the corresponding binary melts.
Abstract: In situ polarized and depolarized Raman spectra of glassy, supercooled, and molten SiO2 have been
measured over the broad temperature range 77â2150 K in an effort to examine possible structural
changes caused by temperature variation. A new experimental setup using a CO2 laser for heating
the sample has been designed allowing measurement with controllable blackbody radiation
background at temperatures up to 2200 K. Careful and systematic relative intensity measurements
and the use of the isotropic and anisotropic Raman representation of the spectra revealed hidden
bands in the bending mode region and resolved bands in the stretching region of the spectra. Overall
the spectra behavior shows similarities with the spectra of the recently studied tetrahedral glasses/
melts of ZnCl2 and ZnBr2. Increasing temperature causes subtle changes of the relative intensities
within the silicon-oxygen stretching region at 750-850 cmâ1 and gives rise to a new band at
930 cmâ1. The spectral behavior is interpreted to indicate that the âSiO4/2â tetrahedra are bound
to each other to form the network by apex-bridging and partly by edge-bridging oxygens. The
network structure of the glass/melt is formed by mixing a variety of tetrahedra participating in
âopenâ cristobalitelike, âclusterâ supertetrahedra, and âchainâ edge-bridged substructures bound
to each other by bridging oxygens. A weak in intensity but strongly polarized composite band is
resolved at 1400 cmâ1 and is assigned to SivO terminal bond frequency. Temperature rise
increases the concentration of the terminal bonds by breaking up the network. These structural
changes are reminiscent of the polyamorphic transformations occurring in silica as has recently been
predicted by computer simulations. At low frequencies the Raman spectra reveal the presence of the
Boson peak at 60 cmâ1 which is well resolved even above melting temperature up to 2150 K.
Abstract: Raman spectra of K2Si4O9 were measured over a broad temperature range including the glassy,
supercooled, and molten states in an effort to follow the structural changes caused by temperature
variation. Potassium tetrasilicate glass has been prepared using a containerless method and a CO2
laser for heating and melting the samples and thus avoiding contamination induced by the walls of
the crucibles. Systematic Raman intensity measurements caused by temperature variation have been
performed in order to elucidate the induced structural changes in the high-frequency stretching and
in the three- and four-membered ring breathing vibration regions. The high-frequency symmetric
stretching vibrations of the nonbridging SiâO bond are associated to the presence of two distinct
types of tetrahedral units with terminal oxygen atoms. The low-frequency Raman spectra reveal the,
well resolved, presence of the boson peak at temperatures above the melting point. The temperature
dependence of the boson peak energy has also been determined and compared with that of the sound
velocities of potassium tetrasilicate. The results are discussed in the context of recent experimental
and theoretical works.
Abstract:
Raman spectra of the 0.1Nb2O5â0.9TeO2 binary glass-forming oxide system were measured over a temperature range including the glassy,
supercooled and crystalline state to reveal the structural changes caused by temperature variation. The analysis of the reduced Raman spectra
made it possible to quantitatively follow the transformation of the TeO4 trigonal bipyramidsâthat dominate in the low temperature glassâinto
TeO3 trigonal pyramids with temperature rise. Based on the predictions of existing structural models, we estimated with the aid of the Raman data
the number of terminal oxygen atoms that inevitably accompany this structural change. The various crystal phases of the system studied in this
work and the routes for converting one crystal phase into another were also examined. Finally, the low-energy excitations of the non-crystalline
states of 0.1Nb2O5â0.9TeO2 were studied by following the temperature dependence of the Boson peak.
Abstract:
The electronic absorption spectra of the hypersensitive transitions 5G6)5I8 of Ho(III) and 4G5/2)4I9/2 of Nd(III) have been measured in
molten LiClâKCl eutectic and in LaCl3âKCl molten mixtures. The ligand field components of the above transitions in octahedral symmetry
have been identified and the molar absorptivity changes with temperature and composition have been measured. The spectra are discussed in
terms of the coordination geometries of the probe cations Ho(III) and Nd(III) in these molten salt solvents. The Boltzmann thermal factor
appears to be responsible in part for the variation of the âhotâ band intensities. The data suggest that the predominant factors affecting the
oscillator strength of the Ho(III) and Nd(III) hypersensitive transitions is the degree of octahedral distortions in conjunction with the overall
charge asymmetry around the LnCl6-3 (Ln=Ho, Nd). It appears that no drastic changes occur in the coordination of the probe cations as we go
from dilute in LaCl3 to pure LaCl3 melts; this suggests that in the host melt the coordination of La(III) is more likely to be six-fold. A further
evidence for the six-fold coordination is given by the measured JuddâOfelt parameters of Nd(III) in both molten NdCl3 and La(Nd)Cl3.
Abstract:
In the current study it is proposed an alternative use of
the laser Raman spectroscopy in the field of ophthalmology,
through the 908 scattering geometry. This spectroscopic
technique gave the opportunity of detecting within the
aqueous humor of the eye antibiotics close to MIC as well as
physiological substances in early pathological levels. It is
emphasized that the direct exposure to the laser light of
basic cordial tissues of the eye, like the lens and retina, is
avoided although an optimum-scattered light collection is
accomplished. It is anticipated that laser Raman spectroscopy
might be proved useful to the field of ophthalmology
for the study of pharmacokinetics and on-time diagnosis of
intraocular diseases (e.g., diabetes), as long as a golden
selection of Raman components concerning collection
optics, spectrograph throughput, resolution, and quantum
efficiency of the CCD detector will be accomplished.
Abstract: Raman spectra of the LaCl3âCsCl melt mixtures at ten different compositions, including solid and molten LaCl3 have been measured at
temperatures up to 900 8C. The systematic spectral changes with composition and the invariance of the spectra on temperature are discussed in
terms of the melt structure and in relation to other lanthanide halideâalkali halide melt mixtures. The data suggest that in CsCl-rich mixtures
the predominant species present are the LnCl 6 ââoctahedraââ while in LaCl3-rich melts a network-like structure of chloride bridged
coordination polyhedra is formed. Most likely the predominant coordination of La(III) remains six-fold at all compositions. The reduced
isotropic and anisotropic Raman spectra are calculated and compared with the recently published simulated Raman spectra of the same melt
mixtures.
Abstract: A temperature dependent Raman spectroscopic study of the Boson peak in silica is being presented. For the first time experimental
data are obtained not only above the glass transition temperature but also above the melting point. The intriguing temperature dependencies
exhibited by the Boson peak frequency and intensity are examined in detail. A comparison of the above features between the
frequency-reduced and the true excess density of vibrational states revealed that the spectrum of the latter does not exhibit the anomalous
trend of the Boson peak as regards the temperature dependence of its frequency, and further the number of the excess modes decreases
with increasing temperature. The observability of the Boson peak in the normal liquid state as a well-resolved peak is also discussed in the
context of recent theoretical and simulation works that relate the Boson peak with the details of the potential energy landscape of the
Abstract:
The composition and temperature dependence of the Raman spectra of molten LnI3-CsI (Ln =Ce,
Dy, Ho) mixtures have been measured. Raman spectra of the polycrystalline compounds CeI3, DyI3,
CS3CeI6,CS3DyI6and CS3DY2I9have also been measured from room temperature up to ~ 750°C,
where melting occurs for most of these salts. The data are correlated to previous studies involving
rare-earth chlorides and bromides and are discussed in terms of the melt structure and the structural
systematics of the rare-earth iodide-alkali iodide molten mixtures.
Abstract: The vapors of NbF5 and TaF5 have been investigated by Raman spectroscopy in the temperature range 475â675 K and at total pressures
from 0.1 to 4.0 atm. The temperature and pressure dependence of the spectra is indicative of equilibrium shifts between monomer and
associated (polymer) gaseous species. The intensities of Raman bands, which were characteristic of the various species present, were
exploited in order to establish the stoichiometry and thermodynamic functions of the reaction nMF5(g) ? MnF5n(g) (M = Nb, Ta). It was
found that unambiguously n = 2 in the studied temperature range, which implied that the predominant vapor species are monomers MF5(g) and
dimers M2F10(g). The thermodynamic functions according to the studied dimerization reactions were measured from the Raman data as: (a)
DHR = 104.3 2.4 kJ mol1, DSR = 175 20 J mol1 K1 for 2NbF5(g) ?Nb2F10(g); (b) DHR = 101.1 3.7 kJ mol1, DSR = 150
30 J mol1 K1 for 2TaF5(g) ? Ta2F10(g).
# 2004 Elsevier B.V. All rights reserved.
Abstract:
Quantitative Raman spectra of molten PbCl2âACl (A = K, Cs) mixtures have been measured at different compositions and at
temperatures up to 680 C. Spectral changes upon melting the Cs4PbCl6, CsPbCl3, KPb2Cl5 and PbCl2 solids have been also mea-
sured. All spectra of melts are mainly characterized by an isotropic (polarized) mP and an anisotropic (depolarized) mD band. The
intensity and position of the mP (237 ± 2 cm1) and mD (113 ± 3 cm1) bands remain practically constant at XPbCl2 6 0:5 indicat-
ing that the structure is predominated by coordination polyhedra of the type PbnCl3n
n (n 6 4). With increasing PbCl2 mole fraction
the mP and mD bands shift to the ââredââ and the ââblueââ, respectively, reaching the corresponding values of 215 and 132 cm1 in pure
molten PbCl2. Furthermore, the intensity ratio of the anisotropic to isotropic spectra increases indicating contributions to the scat-
tering intensity arising from dipoleâinduced-dipole interactions in these melts.
2005 Elsevier Ltd. All rights reserved.
Abstract: Raman spectra of molten binary mixtures of ZnF2âAF (A = K,Cs) and of PbF2âKF have been measured at temperatures up to
1000 C. Composition and temperature dependent measurements are related to the structure of these melts. The changes of vibrational
modes upon melting the polycrystalline compound K2ZnF4 and K4PbF6 have been also measured. For the ZnF2âAF melt
mixtures rich in AF a strong polarized band at 471 cm1 is assigned to the ZnF2 4 tetrahedral species. With increasing ZnF2 mole
fraction the polarized band shifts to high frequencies by 10 cm1 indicating the formation of either a trigonal ðZnF3 à and/or
bridged tetrahedral ðZn2F2 6 à species. These species are also present in ZnF2-rich melt mixtures in equilibrium with a variety of
distorted octahedral ðZnF4 6 à species with a characteristic polarized band at 364 cm1. Most probably the structure of very rich
in ZnF2 melts and of pure molten ZnF2 is predominated by bridged octahedra forming a loose network. The spectra of PbF2âKF
melt mixtures show mainly one polarized band at 400 cm1 whose position is practically independent of composition. It appears
that in KF-rich melt mixtures the structure is predominated by independent anionic species PbmFn 2mþn of unknown stoichiometry and
symmetry. With increasing PbF2 mole fraction the anionic species interact with each other by sharing fluorides and forming larger
structures with short lifetimes. The relative intensities of the isotropic and anisotropic spectra of both sets of the ZnF2âKF and
PbF2âKF binaries have been calculated and are correlated to cation shielding effects and to dipole-induced dipole interactions in
these melts.
Abstract: Raman spectroscopy has been used to elucidate the structure of ScCl3âCsCl molten mixtures in the complete
composition range and at temperatures up to 1000 C. The variation of temperature and composition reflected
systematic changes in the spectra which were interpreted in terms of structural changes in the melts. In mixtures
with ScCl3 mole fractions below 0.5 the melt structure was predominated by a series of ionic species ScCl7 4-
ScCl6 3-, Sc2Cl9 3- and ScCl4 - which established different chemical equilibria. At melt compositions rich in
ScCl3 the isotropic Raman spectra are characterized by two bands P1 and P2. The position and relative intensities
of these bands change with composition in a similar way as observed previously in studies of other rare earth
halide systems. Furthermore, the continuous shift of the P2 band with composition is in accordance with the
recent computer simulations [P. A. Madden, M. Wilson and F. Hutchinson, J. Chem. Phys., 2004, 120, 6609]
which give an understanding of the origin of this band. A cluster-like model is proposed for the structure of
molten ScCl3 where fragments of scandium ââoctahedraââ bridged by chlorides are terminated with scandium
ââtetrahedraââ having terminal chlorides.
Abstract:
A Raman scattering study is presented in an effort to determine the structural changes that take place when
modifying silica glass with an alkaline earth oxide modifier. Glasses have been prepared from the binary system xCaOâ
(1-x)SiO2 (x =0, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, where x is the molar ratio of CaO) using a containerless methodto
melt andquench the samples. In the concentration region 0:3 < x < 0:45 the spectra show that the structure differs from
that of silica but no appreciable changes â either in relative intensities or shifts of vibrational bands â between various
compositions are detected. For x > 0:45 structural changes take place as indicated in modifications of peak relative
amplitudes and Raman shifts. The frequency of the Boson peak and the defect peak (D2) change when crossing the
x =0:45 point. The obtained results are discussed in the framework of existing structural models of silica and modified
silica glasses andare suggestive of a microphase separation near the peritectic composition of the binary system.
Abstract: Glassy, supercooled, and molten ZnCl2 and ZnBr2 have been studied by Raman spectroscopy over
the broad temperature range 2196 to 800 °C in an effort to follow in detail the structural changes
caused by temperature variation. A systematic study has also been undertaken for the corresponding
crystalline polymorphs showing that each material exists in only one crystalline phase if water traces
are not present. The reduced isotropic and anisotropic Raman spectra of the ZnCl2 and ZnBr2
glasses and melts are isomorphous. Unusually drastic changes of the relative intensities of particular
bands occur with temperature in the reduced isotropic spectra. A comparison between the spectral
features of crystals, glasses, and melts has revealed that the network structure of the glasses and
melts consists of ZnX4/2 (X5Br,Cl) tetrahedra bound to each other by apex- and edge-bridged
halides. The substructure of the glass/melt is formed by mixing a variety of tetrahedra participating
in ââopen,ââ ââcluster,ââ and ââchainââ networks which are bound to each other by bridged halides. The
boundaries of the substructure involve neutral or charged terminal halide bonds with zinc of an
average threefold coordination. Temperature rise breaks up the substructure to smaller fragments,
increases the number of terminal bonds, and rearranges the apex- and edge-bridging networks. The
good glass-forming ability of the ZnX2 melts is attributed to the existence and mixing of the three
topologically different networks within the substructure. Our data of ZnCl2 are in qualitative
agreement with molecular dynamics simulations as regards the frequency distribution of vibrational
modes. However, simulations are not able to correctly predict polarization properties in the glass and
the melt. The low-frequency Raman spectra reveal the presence of the Boson peak in both glasses,
which interestingly persists, well resolved, also into the normal liquid state above the melting point.
The spectra in the region of the Boson peak are also discussed in the framework of relevant
theoretical models and empirical correlations.
Abstract:
Raman scattering has been employed to study the temperature and polarization dependence
of the vibrational modes for the glass-forming halide salt mixtures xZnCl2-(1 ? x)AlCl3, with
x = 0.8 and 0.6. The analysis has shown that the vibrational modes of the mixtures arise from a
contribution of the vibrational modes of the pure components salts. Emphasis has also been given
to the low-frequency modes (3 - 80 cm?1), and particular points related to the glass transition
phenomenology are discussed in view of the experimental findings.
Abstract: Low-frequency (5â120 cm-1) Raman scattering has been utilized to elucidate the temperature and polarization
dependence of the quasi-elastic line and the Boson peak of the glass-forming salt 0.8ZnCl2â0.2AlCl3. A combined
analysis, including both polarized and depolarized spectra, is being presented aimed at elucidating the frequency de-
pendence of the scattered intensity at these low frequencies. The depolarization ratio of the pure Boson peak, after
being disentangled form other contributions, namely the quasi-elastic line and low-lying vibrational modes, has been
determined. The results reveal that the individual depolarization ratio of the Boson peak is strongly frequency de-
pendent and different from the depolarization ratio of the quasi-elastic line. The temperature dependence of the quasi-
elastic scattering intensity and of the maximum of the Boson peak has also been determined. The results are discussed in
the framework of the current phenomenological status of the field.
Abstract: A temperature-dependent, sub-band-gap, light-scattering study of the vibrational modes of vitreous As2S3
fibers during the photoinduced fluidity effect is reported. The structural changes that give rise to the effect are
detected mainly through variations in the degree of polarization of the scattered light. The results show a
nonmonotonic behavior in the observed structural changes interpreted as a reduction in the flow ability of the
glass a few degrees above room temperature followed by a subsequent increased ability to plastic deformation
at higher temperatures, but still well below the glass-transition temperature. Studies on the nonstoichiometric
concentration As25S75 at room temperature revealed noticeable differences with arsenic trisulfide. The relation
between the illuminating energy and the band gap of the glass has also been investigated. An account for the
possible nature of these experimental facts is attempted in terms of the specific structural units constituting the
glass structure.
Abstract: Raman spectroscopic measurements of ScCl3âCsCl molten
mixtures in the temperature range of 600â900 C and
compositions up to 25 mol% ScCl3 indicate that the
predominant scandium(III) chloroions in these melts are
ScCl36- and a novel all chloride highly coordinated ScCl47-.
Abstract: The picosecond dynamics of molten alkali halides is discussed, and the low-frequency Raman
spectra of molten LiCl, CsCl, and the LiClâCsCl eutectic are fitted to the model enabling to obtain
the times of vibrational dephasing, t V and vibrational frequency modulation tv . In terms of the
Wilmshurst criterion @J. Chem. Phys. 39, 1779 ~1963!# and using the data of NMR studies and
molecular dynamics simulations, a conclusion is drawn that molten alkali halides cannot contain
long-lived stable complexes with lifetimes greater than 1028 s. The low-frequency Raman spectra
of molten alkali halides and their mixtures probe the presence of instantaneous spatial configurations
of MXn
2n11 type, where M1 is the alkali metal cation and X2 is the halide anion existing in melts
during the time intervals equal to the time of duration of collision of oppositely charged ions t d ,
which is less than 0.5 ps. This time is sufficient to a collision complex to execute several ~at least
one! vibrations. Vibrational dephasing and modulation processes elapse during this same time,
thereby indicating the instantaneous nature of configurations in question. To discern between
short-lived and long-lived complexes, we propose relations between the minimal damping time of
the probe oscillator set equal to the half-period of vibration T/2, t V , tv , and t d , as well as the time
between collisions t BC . The duration of an act resulting in the vibrational phase shift ~or energy
transfer! must be equal to ~or longer than! the half-period of vibration of the probe oscillator, t V
>T/2. The modulation time may vary from this same half-period of vibration or the time between
collisions t BC to very long times, tv>T/2, tv>t BC . For short-lived complexes, the longest of two
characteristic times describing the phase decay cannot exceed possible duration of collision, tv
<t d , t V<t d . Cs-containing configurations follow this definition and therefore should be
considered instantaneous short-lived collision complexes: their t V'T/2;0.1 ps, and tv't BC
;0.03 ps. Li-containing configurations appear to be relatively long-lived: their lifetimes could be
associated with tv;0.17 ps, which is several times longer than any other shortest possible
characteristic time in the system ~t BC;0.026 ps or T/2;0.05 ps!. In light of these conclusions, an
a priori assumption of autocomplex MX4 n24 anions and Mn1 cations as being structural elements of
molten halides made in the so-called autocomplex model by Smirnov, Shabanov, and Khaimenov
@Elektrohim. 2, 1240 ~1966!# is discussed, and the autocomplexes are identified as instantaneous
short-lived configurations detectable by the Raman method.
Abstract: The solubility of Nb(V) as a function of O composition in the ternary eutectic LiFâNaFâKF (FLiNaK) melt at 7008C has been
determined. Raman spectra at different oxide concentrations and temperatures were recorded. Based on chemical analysis of melt samples and bands in the spectra suggestions related to the NbâOâF complex formation are given. The addition of Na2O to FLiNaK containing 0.22 mole kg-1 K2NbF7 show that at: no/n Nb less than 2 there is no precipitation of Nb(V) compounds. The Raman spectra of the melt indicated the presence of monomeric NbF7 2- at low oxide concentrations, which reacted with oxide to form monomeric NbOF2 5- when r was increasing. Further additions of Na2O formed the NbO2F4 3- species having a maximum concentration at nO/nNd =2; when 2 24 O Nb 22 2,n /n ,3, a solid of the type AlkNbO3 was formed. At n /n =3, a minimum in the Nb(V) and O 2- solubilities were observed, but O Nb 3 O Nb the structure of the species in the melt were uncertain. At higher oxide content the AlkNbO3 (s) previously formed was dissolved, possibly with the formation of both corner and edge sharing distorted NbO6 octahedra. The solubility of Nb2O5 in FLiNaK was measured as a function of temperature (550â800C), and the dissolution mechanism seems to be given by the reaction: Alk 1+ +Nb2O5(s) +4F- =Nb2O2F4 3- +AlkNbO3(s). ÎH for the reaction (based on concentrations in mole kg ) was found to be ~90 kJ mol-1 K -1.
Abstract: We report on a sub-band gap light scattering (Raman) investigation for a-As2S3 fibers subjected to external elongation
stress in order to elucidate the photoinduced #uidity e!ect on a microscopic scale. Changes in the short-range order
caused by the presence of the illuminating light have been detected. On the other hand, subtle modi"cations are revealed
in the intermediate range order, manifested in the increase of the magnitude and in the modi"cation of the frequency
dependence for the depolarization ratio } in the low-frequency part of the spectrum } as a function of the applied stress.
The `buckling modela proposed to account for the optical absorption tails in chalcogenide glasses seems quite relevant
for explaining certain aspects of the experimental data.
Abstract: A subbandgap light scattering investigation of vitreous arsenic trisulfide, v-As2S3, fibers subjected to external
elongation stress has been undertaken in order to elucidate the photoinduced fluidity effect @H. Hisakuni
and K. Tanaka, Science 270, 974 ~1995!# in a microscopic scale. Orientational changes in the short-range order
~intramolecular vibrations! caused by the presence of the illuminating visible light are detected. Subtle but
noteworthy alterations are revealed in the intermediate range order, manifested as the increase of the magnitude
and the modification of the frequency dependence of the depolarization ratioâin the low frequency part of the
spectrumâas a function of the applied stress. The results are discussed alongside with old and recent structural
models that have been employed to account for light-induced changes in amorphous semiconductors and
low-energy modes in amorphous solids.
Abstract: Isotropic and anisotropic Raman scattering spectra of molten LiF, KF, and CsF and of molten mixtures KF-LiF and CsF-LiF have been measured at temperatures up to 900 C. For the single component molten salts the reduced representations of the spectra show one anisotropic and two isotropic bands. The data are discussed and interpreted in terms of interaction induced polarisability fluctuations. The dipole-induced-dipole interactions predominate the CsF anisotropic spectra while polarisability fluctuation due to anion-cation
overlap interactions give rise to the strong isotropic scattering in LiF. The anisotropic Raman scattering intensity from the binary mixtures appears to be a superposition of the corresponding intensities of the component salts, while the isotropic spectra are characterised by a new band at ~325 cm-1 which is common for both the KF-LiF and the CsF-LiF binaries. The origin of this band is attributed to the formation of long lived associated configurations of the type (LiFx)A, (A=K, Cs) in the melt mixtures.
Abstract: Raman spectra of solid and liquid beryllium chloride and of binary liquid BeCl2-CsCl mixtures have been measured. Systematic investigation of the Raman spectra upon heating the crystalline forms of BeCl2 revealed two different solid phase transitions at 350 and 405 C. A glass phase was also obtained by vapour transport with a crystallisation temperature at ~250 C. The Raman spectra of the molten and glassy BeCl2 show bands at common frequencies that are correlated to certain vibrational modes of two solid allotropic phases.
Temperature dependent measurements of the Raman spectra of a series of BeCl2-CsCl melt compositions suggest that : (a) at BeCl2 mole fractions lessthan 0.5 the liquid structure is predominated by tetrahedral and trigonal beryllium
species in equilibrium, and (b) at mole fractios greater than 0.5 two types of polynuclear beryllium ionic species are formed, one consisting of a chain of edge-bridged BeCl4 tetrahedra and the other having a cluster like structure of vertex-bridged BeCl4 tetrahedra. The spectra of pure BeCl2 liquid and glass are interpreted in terms of similar neutral chain and cluster structures having as ending units trigonally coordinated beryllium atoms. On going from the glass to the melt and/or with increasing temperature the cluster structures unfold to form chains. Similarities also exist between the structures of molten BeCl2 and of glassy SiSe2 .
Abstract: The coordination environment around Gd3+ ions in GdAl3Cl12 glass and supercooled
liquid has been studied using Gd LIII -edge EXAFS spectroscopy. The Gd coordination
environment in the glass is found to be similar to that in the GdAl3Cl12 crystal with eight Cl
nearest neighbours and four Al next-nearest neighbours. The GdâCl distance in the glass is the
same as that in the crystal (â¼2.8 Ã) although the GdâAl distance in the glass (â¼3.85 Ã) is longer
than that in the crystal (â¼3.7 Ã), indicating a less dense structure with a larger GdâClâAl bond
angle in the former. The GdâCl distance and coordination number are found to remain unchanged
in the supercooled liquid at 60 â¦C. However, the absence of any GdâAl second-neighbour shell
in the EXAFS spectrum of the liquid indicates substantial increase in static disorder in the spatial
disposition of AlCl4 tetrahedra around Gd in the liquid. Such temperature dependent structural
changes are suggested to be responsible for the marked fragility of this liquid.
Abstract: Specific information extracted from low-frequency Raman data, for a widely varied in chemical nature class
of inorganic glass formers, are presented showing the weakness of the basis on which relevant current models
and phenomenological correlations rely. The three pertinent issues of the field, namely, relaxation to vibration
contribution, the frequency dependence of the depolarization ratio, and the low-frequency behavior of photonphonon
coupling coefficient are discussed in light of nontrivial data for strong, fragile, and intermediate
glasses. It is shown that putative well-known universalities, e.g., the correlation of the strong or fragile
character of a supercooled liquid with the strength of the fast dynamics and the frequency independence of the
depolarization ratio in the low-frequency Raman region are not well established, due to the limited consideration
of experimental data.
Abstract: The structure of molten mixtures of GdCl3-KCl at different compositions and temperatures has been
investigated by f^f electronic absorption and Raman spectroscopy. The systematics of the Raman spectra
indicate that in melt mixtures rich in KCl the predominant species are GdCl63- octahedra, while at higher
GdCl3 mole fraction edge bridging of the octahedra occurs. At all compositions including the pure melt 3 GdCl3 the gadolinium coordination is presumably six-fold. The electronic absorption spectra of Ho3+in molten LiCl,
CsCl and LiCl-KCl eutectic have been measured. The data suggest that the predominant factor affecting the
intensities of the Ho3+ hypersensitive transitions is the degree of octahedral distortions in conjunction with the
overall symmetry around the HoCl63-Changes of the electron donating ability of the Clligands by the .
polarizing power of the alkali metal counter cations do not affect drastically the f^f intensities. Electronic
absorption spectral measurements of Ho3` centers in different GdCl 3-KCl molten mixtures show that the
hypersensitive band intensities increase with increasing GdCl 3mole fraction. These changes are attributed to increasing octahedral distortion imposed on the HoCl63-octahedra by the host melt. Furthermore, the
spectra indicate that there are no drastic coordination changes occurring as we go from the mixtures dilute in
GdCl 3 to the pure GdCl3 melt, and support the Raman data view that the coordination of Gd3` is six-fold at all compositions.
Abstract:
Micro-Raman spectroscopy is used to characterize the cemented product formed during cobalt
cementation with zinc dust in zinc sulfate electrolytes. The effect of copper and antimony on the
cementation process is also examined. A Raman spectrum characteristic of a basic cobalt salt or
mixtures of such salts is observed. The spectrum is similar to those found for CoOH.2 in a ZnO
matrix. The main Raman band of this salt has a frequency at 550 cmy1. Raman mapping over a
larger area, 1000=1000 mm, of cemented products shows that the occurrence of this peak
decreases dramatically during re-dissolution of cemented cobalt. The data indicate that a large
fraction of the cemented Co2q exists as a mixture of cobalt containing oxide and hydroxide.
Abstract: The molecular orientation of uniaxially drawn commercial poly(vinyl chloride), PVC,
specimens has been investigated by polarized Fourier transform infrared (FTIR) in the specular reflectance
mode and by resonance Raman scattering in various combinations of sample orientation, scattering
configuration and polarization geometry. The orientation was examined as a function of the specimen
draw ratio. The Kramers-Kronig transformation has been used to obtain infrared absorption spectra
from the FTIR reflectance data; the orientation was determined by the dichroic ratio of the C-Cl stretching
and CH2 rocking modes of PVC. The resonance Raman spectra of polyene segments that result from
partial thermal degradation/dehydrochlorination of PVC during processing have been utilized in order
to determine the parameters of the orientation distribution function. The all-trans conjugated polyene
sequences formed during degradation are considered as rodlike segments in the polymer backbone and
are used as indicators of orientation within the amorphous-like polymer phase. As far as the trends are
concerned, data analysis showed good agreement between FTIR and Raman results regarding the induced
molecular orientation in industrial PVC specimens.
Abstract:
The dynamic properties of glassy and liquid As2O3 are investigated over a wide temperature range, in both the microscopic and macroscopic time domains by Brillouin scattering (BS) and photon correlation spectroscopy (PCS). The two characteristic properties of sound propagation, velocity, and attenuation were found to exhibit considerable, although unexpected, changes very close to the glass transition temperature Tg . The high-frequency density fluctuations were quantitatively treated using a phenomenological formulation for the corresponding memory function, which considers both slow and fast processes. The obtained viscoelastic parameters were found to follow physically acceptable temperature dependencies. Both density and orientation autocorrelation functions show a very narrow distribution of relaxation times with a shape parameter close to 0.8. The peculiarities of the sound-velocity and the sound-absorption coefficient as well as the comparison between the PCS and the BS relaxation times confirmed the existence of two relaxation processes differing by 10 orders of magnitude near Tg . The difference in activation energies, for the fast process, between strong and fragile glasses is discussed on the basis of the stability of asymmetric double-well potentials over a relaxation period. Evidence is provided conforming to the two fluid model predictions, invoking long-range density fluctuations. Pseudotransformations of chemically and topologically ââacceptableââ structures seem to be the driving force for low-energy excitations in network bonded glasses.
Abstract: Raman spectra of dark brown-black iron(III) chloride melts have been obtained at 600 K using resonance and micro-Raman techniques. The main polarized bands seen in the spectra are at 310, 414 and 452 cm-1 and their relative
intensities depend on the frequency of the laser excitation line. The data are interpreted to indicate that the predominant species in the melt are Fe2Cl6 bitetrahedral molecules plus charged molecular species which are formed according to the dissociation scheme: 2Fe2Cl6=Fe2Cl5+ +Fe2Cl7-. The proposed liquid structure accounts for both the near ionic conductivity of the melt and the average coordination number of iron(III) in the melt, found to be ~3.8 by neutron diffraction.
Abstract: Raman spectra of Cs2NaScCl6, Cs3ScCl6, Cs3Sc2Cl9 and ScCl3 compounds have been measured from 25C to temperatures above their melting points. The vibrational modes of the discrete species ScCl63- and Sc2Cl93- in the solids are
transferred upon melting into the liquid and participate in an equilibrium involving ScCl4-. The spectra of solid ScCl3are dominated by the vibrational modes of a triple layer of ions consisting of edge-sharing ScCl63- octahedra. Two main bands are seen in the melt spectra which infer a molecular liquid but a rather complex melt structure is suggested by the overallphysicochemical data.
Abstract: Raman spectroscopy has been used to elucidate the structure of molten iron(III) chloride and its binary mixtures with caesium chloride. In order to overcome difficulties arising from the dark coloration of these melts and to ensure the spectral features, both conventional resonance Raman and micro-Raman spectra have been obtained. The spectral changes upon melting the solids Cs2NaCl6, CsFeCl4 and FeCl3 have beenmeasured. The FeCl4- tetrahedra were found to be present in both the solid and molten CsFeCl4 ,while a change of coordination from six-fold (FeCl63-)to four-fold (FeCl4-)occurs upon melting Cs2NaFeCl6 .The FeCl4- tetrahedra are the predominant species in CsCl-FeCl3 mixtures containing up to 50 mol% FeCl3.The systematics and the temperature dependence of the spectra of the molten mixtures with mole fractions from 50 to 100 mol% FeCl3 indicate the presence of Fe2Cl7-, FeCl2+ and Fe2Cl5+ ionic species. Resonance Raman spectra of molten FeCl3 were measured and compared with the spectra of the corresponding solid and vapor. The data are interpreted to indicate a self-ionization of the molecular Fe2Cl6 melt::2Fe2Cl6=Fe2Cl5++Fe2Cl7- .The proposed model accounts for both the near-ionic conductivity of the melt and the structural data obtained by neutron diggraction.
Abstract: Raman spectra of molten ThCl4âACl (A = Li, Na, K or Cs) mixtures have been measured. The complete composition range has been studied for all systems at temperatures up to 960 C. The spectral changes upon melting the binary
compounds A2ThCl6, A3ThCl7 and the pure crystalline ThCl4 were also measured. The data indicate that in molten mixtures rich in alkali-metal chloride the predominant species are the ThCl62- octahedra [ν1(A1g) 297 and ν5(F2g)
125 cm-1] in equilibrium with the ThCl73- pentagonal bipyramid. With increasing ThCl4 mole fraction above 0.3 the frequency of the ν1(A1g) band increases continuously reaching its maximum (~340 cm-1) in pure molten ThCl4.
It appears that in mixtures rich in ThCl4 edge bridging of thorium(IV) octahedra occurs yielding chain species of the type [ThnCl4n-+2]2- and [ThnCl4n+ 2]2- where the end Th atoms of the chain are six- and four-fold co-ordinated
for the anion and cation respectively. The known ionic character of these melts suggests that the chain length is rather small and that most probably the species have low n values (e.g. Th2Cl102-, Th3Cl12-, Th3Cl102-, . . .). Glassy
ThCl4 was formed by slow cooling of the melt. The vibrational modes and the inferred structure of the glass are similar to those of the melt.
Abstract: The structural properties of the cadmium species formed by dissolution of cadmium metal in molten cadmium halides (CdX2:X=Cl, Br, I) and in molten mixtures of cadmium chloride with alkali chlorides have been investigated by Raman spectroscopy. The data indicate that in these ionic solvents the predominant species present is the solvated Cd22+ subvalent cation. With increasing ionic strength of the counter anion the frequency of the diatomic cation shifts from 158 cm-1 for the chloride melt to 183 cm-1 for the iodide melt. Due to the overlap of the electronic absorption edge of the Cd22+ with the laser lines used to excite the spectra the Raman band intensities of the solute species are preresonance enhanced. The dissolution of cadmium metal in the cadmium chloride-alkali chloride mixtures increases with temperature and depends on the stability of the CdCl4 2- species formed in these melts. The looser the association the higher the solubility and the stability of the Cd22+ species. Raman spectroelectrochemical methods have been applied for studying amorphous carbon electrode surfaces during electrolysis of CdCl2 in LiCl-KCl eutectic. A new Raman band measured at ~158 cm-1 during electrolysis was attributed to the subvalent Cd22+species. It seems that these species are formed in the vicinity of the electrode by a homogeneous electrochemical reaction.
Abstract: Raman spectra of liquid and gaseous zirconium tetrachloride and of molten ZrCl4âCsCl mixtures have been measured. Changes of the relative Raman intensities in the vapor phase, near and above the critical point, have established the dimerization reaction 2ZrCl4(g)= Zr2Cl8(g), DHR = 256.6 ± 1.1 kJ /mol. Spectra of solid and molten zirconium chloride show that in the liquid phase ZrCl4 monomers are present in equilibrium with polymerlike (ZrCl4)n species. A systematic investigation of the Raman spectra of the solid mixtures formed upon cooling the ZrCl4âCsCl melts at different compositions has shown that apart from the known Cs2ZrCl6 a new compound with stoichiometry CsZr2Cl9 is also formed. The spectra of solid and molten Cs2ZrCl6 and CsZr2Cl9 show that
ZrCl622-and the Zr2Cl92- are present in both phases. In molten ZrCl4âCsCl mixtures and at compositions X(ZrCl4) < 0.33 the ZrCl62- octahedra are predominant. In the range 0.33 < X(ZrCl4) < 0.66 the spectral changes with
temperature and composition reflect an equilibrium involving three ionic species: ZrCl62-, Zr2Cl9- and Zr2Cl102-(or ZrCl5-). At mole fractions rich in ZrCl4 (X> 0.66) the spectra indicate an equilibrium between the ionic Zr2Cl92-, the ZrCl4 monomer and the (ZrCl4)n polymer-like species. All data suggest that the value of n is small and most probably hexamers and/or dimers are the predominant âpolymerâ species in these melts.
Abstract: Raman spectra of the following rare earth halideÃalkali halide binary molten salt systems have been measured: LnBr3-KBr(Ln=La, Nd, Gd) and NdCl3-ACl(A=Li, Na, K, Cs). The complete composition range has been studied at temperatures up to 850 C. The spectral changes occurring upon melting the elpasolite compounds Cs2NaLnBr6(Ln=La, Nd, Gd) andCs2NaNdCl6 and the pure crystalline solids LnBr3(Ln=La, Nd, Gd) and NdCl3 were also measured. The data indicate that the behavior of these melt mixtures is similar to those of the YX3 - KX (X=F, Cl, Br) binaries studied before. In molten mixtures rich
in alkali halide with lanthanide halide mole fractions less than 0.25, the predominant species are the LnX63-octahedra giving rise to two main bands P1 (polarized) and D1(depolarized) which are assigned to the v1(A1g) and v5(F2g)octahedral modes. In molten mixtures rich in LnX3 the spectra are characterized by the P1 and D1 bands plus two new bands D2(depolarized) and P2 (polarized). The P2 band shifts continuously to higher frequencies with increasing LnX3 content. These four bands are attributed to the D3 distortions of the octahedra bound by edges in the melt. The room temperature Raman spectra of the LnX3 solid compounds were characterized by bands due to the vibrational modes of the different crystalline structures : hexagonal for
LaBr3 and NdCl3 orthorhombic for NdBr3 and rhombohedral for GdBr3 having the Ln3+ coordination number (CN) or 9, 8 and 6, respectively. With increasing temperature the spectra of the GdBr3 solid are dominated by six Raman bands which are assigned to the vibrational modes of a triple layer of ions consisting of distorted octahedra GdBr63- (CN=6) which share edges with neighboring octahedra. Upon melting, the molar volume of GdBr3 does not change much and the spectra are characterized by the above-mentioned P1, P2, D1 and D2 and bands and can be correlated to the triple layer modes of the solid. The high temperature spectra of the hexagonal LaBr3, NdCle and the orthorhombic NbBr3 show that the structure and CN remain the same up to melting. However, upon melting, the compact orthorhombic (CN=8) and hexagonal (CN=9) forms increase drastically their molar volume and give spectra similar to those of molten GdBr3,YBr3 and YCl3 and where the Ln3+ is in a six-fold coordination (CN=6). It appears that the structures of all the LnX 3melts are similar and independent of the structure of the solids. The frequency changes upon melting the LnX 3 solids, the presence and assignment of the3P1, P2, D1 and D2 bands in the spectra, the continuous shift of the P2 band with composition in the LnX3-AX binaries and the correlation of the high temperature modes of the rhombohedral LnX3 solid (CN=6) to the liquid suggest that the loose network structure proposed for the LnX3 melts is more likely to arise from triple layer like structures composed of distorted octahedra. The rigidity of the network is related to the splitting of the P1 and P2 bands and increases with increasing distortion of the octahedra in the sequence La to Y; L to Br. Fast interchange of ions leads to short lifetimes for the octahedra and weak intralayer interactions.
Abstract: Raman spectra of a series of LnF3 (Ln=La, Ce, Nd, Sm, Dy, Yb)-KF binary melt mixtures have been measured at temperatures up to 1000 C and at compositions up to 40 mol.% for the mixtures with La and Ce and up to 25 mol.% for the remaining mixtures. The data indicate that at mole fractions X (laF3) less than 0.25 the octahedra LnF63- are the predominant species giving rise to
two main bands, one polarized, the other depolarized, which are assigned to the v1(A1g) and v5(F2g) vibrational modes of the octahedra, respectively. The v1 frequency varies almost linearly with the polarizing power of the lanthanide cation increasing from 445 cm-1 (Yb) to 400 cm-1 (La). Such a variation has not been observed in the corresponding binary melts involving chlorides and bromides; it is argued that the relative shielding of the Ln3+ by the anions are responsible for this behaviour. At mole fractions X greater than 0.25 the features of the reduced isotropic and anisotropic spectra are similar to those of the YF3-KF(Dracopoulos, B. Gilbert, B. Borresen, G. Photiadis and G. N. Papatheodorou, J. Chem. Soc., Faraday T rans., 1997, 93, 3081).
One polarized and two depolarized bands appear in the spectra which are interpreted to indicate that the predominant vibrations in these melts arise from distorted LnF63- octahedra bound by common fluorides (edge sharing). The anisotropic scattering intensity was found to increase, relative to the isotropic intensity, with both increasing the size and mole fraction of the lanthanide
cation. This unusual eggect is attributed to dipole-induced-dipole interactions between cations in the melt and its variation from system to system is related to the size and polarizability of the Ln3+ cation and its relative shielding by the F- anions.
Abstract: Raman spectra of liquid mixtures of the NdCl3-NdOCl binary confirm that the network-like structure of chlorine edge-sharing NdCl63- octahedra in pure liquid NdCl3 is not changed significantly by the addition of NdOCl. Freezing-point depression data at the NdCl3 (l/s) phase boundary confirm this conclusion, and suggest that O2- ions are built into this structure as NdnOCl3n+24- anions with n greater than or equal to 2.
The published phase diagram of the NdCl3-Nd2O3(NdOCl) system is not in agreement with the present data, showing smaller Nd2O3(NdOCl) solubilities together with higher melting points at the NdCl3(l/s) boundary than the published data.
Abstract: Raman spectra of the following binary molten salt systems have been measured: (a) YBr3-ABr (A = Li, K, Cs) at temperatures up to 920 degrees C and at different compositions; (b) YF3-KF at temperatures up to 1000 degrees C and compositions up to 50% YF3. The spectral changes occurring upon melting of Cs2NaYBr6, YBr3 and K3YF6 crystalline compounds were also measured. The data indicate that, in mixtures rich in alkali halide, YX63-(X = F, Br) octahedra are the predominant species giving rise to two main bands P-1 (polarized) and D-1 (depolarized) which are assigned as follows: (a) YBr63-, P-1 = 156 cm(-1), v(1)(A(1g)) and D-1 = 78 cm(-1), v(5) (F-2g); and (b) YF63-, P-1 = 445 cm(-1), v(1)(A(1g) and D-1 = 225 cm(-1), v(5)(F-2g). In molten mixtures rich in YBr3 in addition to the P-1 and D-1 bands a new depolarized D-2 (ca. 210 cm(-1)) and a strong new polarized P-2 band appear in the spectra. The P-2 band shifts from ca. 200 cm(-1) to ca. 250 cm(-1) with increasing YBr, content. The presence of these four bands and their polarization characteristics suggest that the predominant vibrational modes in the YBr3-rich mixtures are due to a close C-3v pyramidal like 'unit' arising from the D-3 distortions of the YBr63- octahedra bound by edges in the melt. This behaviour, as well as the spectral changes upon melting YBr3, supports the view that the structure of pure molten YBr3 consists of edge-sharing distorted octahedra. The molten fluoride mixtures YF3-KF at composition X-YF3 > 0.25 also show four bands, two depolarized at ca. 240 cm(-1) (D-1), ca. 370 cm(-1) (D-2) and two overlapping polarized bands at ca. 440 cm(-1) (P-1), ca. 460 cm(-1) (P-2). Finally, the trends of the YX3-KX spectra on going from the bromide to chloride to fluoride melts suggest that pure molten YF3 is likely to possess a loose 'network' structure of edge-bridged distorted octahedra as in the case of molten YCl3 and YBr3.
Abstract: Photon correlation spectroscopy in both polarized and depolarized geometries has been utilized to study density and orientation fluctuations in ZnCl2, ZnBr2, and their symmetric mixture in the metastable supercooled state. The pure components display behavior intermediate between strong and fragile glasses reflected in the shape (L(log t)) and dynamics (t) of the relaxation function C(t), being similar for both density (CF(t)) and orientation (C2(t)) correlation functions. In contrast to polymer blends, concentration fluctuations have no measurable broadening effect on the shape of C(t). Instead, L(log t) becomes narrower with increasing temperature and affects differently CF(t) and C2(t) for the zinc halide mixture. Despite local homogeneity in the thermodynamically ideal mixture, ZnBr2 with the higher glass transition temperature (Tg ) 395 K) was found
to dominate the primary R-relaxation in the symmetric binary mixture. In the framework of âtwo-fluidâ models, the distribution and the temperature dependence of ô support rigid microheterogeneities on the order of 2 nm. The additional slow process, observed in fragile glasses so far,appears to affect also the anisotropic scattering from the pure components.
Abstract: The liquid to glass transition for arsenic trioxide has been studied by performing low-frequency Raman scattering in the temperature range 300-770 K, For this glass forming system the light scattering intensity ratio of the relaxational (omega < 15 cm(-1)) to the vibrational (Boson peak) contribution is much higher than that expected for low fragility systems near the glass transition temperature. A possible explanation for this unexpected feature is given by employing a structural model that is also able to interpret the hypersound propagation and absorption peculiarities found previously in this system. The depolarization ratio, in the quasi-elastic frequency region for different oxide glasses, is associated with local microstructural transformations causing fast relaxations in these systems. The Boson peak region is discussed in the context of different models and current theoretical approaches for the glass transition. (C)
Abstract: The dynamics of density fluctuations in arsenic trioxide has been investigated by Brillouin and photon correlation spectroscopy over the broad temperature range of 370-770 K. Over overlapping temperature ranges, a fast secondary and slow primary (alpha) relaxation were clearly resolved with a time separation of about ten orders in magnitude. The former observed in the GHz frequency range appears to be of a different origin from the beta relaxation that is usually probed by dielectric spectroscopy in the glassy state. Conformational transitions between specific liquid structures are evoked to rationalize these fast density fluctuations in the supercooled amorphous state.
Abstract: Raman and UV/VIS spectra were obtained at temperatures up to 625 K for the gas-phase complex formed over POCl3-FeCl3 molten mixtures under static equilibrium conditions. Raman spectra were also measured for molten POCl3-FeCl3 salt mixtures. A comparison of the spectral features of the POCl3-FeCl3 vapours with those of the POCl3-FeCl3 molten mixtures at 525 K indicates that the gas-phase complex has a 1:1 stoichiometry (POCl3 . FeCl3) with characteristic vibrational bands at 95, 362, 530, 1218 and 1268 cm(-1). The data indicate a C-3v symmetry for the POCl3 . FeCl3 complex. The energies of the M<--t charge-transfer transitions in the electronic absorption spectra of the POCl3 . FeCl3 gas-phase complex suggest, in agreement with the Raman data, that complexing occurs through oxygen bridging. The 1:1 POCl3 . FeCl3 molecular liquid complex is the predominant species in equilibrium with POCl3 and iron chloride at temperatures around 500 K. At temperatures below 450 K and in POCl3-rich mixtures the '3:2' ionic liquid compound [Fe(POCl3)(6)][FeCl4](3) was formed at the expense of POCl3 . FeCl3 (I). Two solids were identified at room temperature,yellow POCl3 . FeCl3 and red [Fe(POCl3)(6)][FeCl4](3), and their Raman spectra have been recorded.
Abstract: Molten mixtures of lithium chloride and cesium chloride have been studied using Raman spectroscopy at temperatures up to 850 °C. Reduced isotropic and anisotropic Raman relative intensities have been measured at different compositions and temperatures. The spectra of the mixtures show two bands with ââcharacteristicââ frequencies vCs and vLi close to the frequencies of
the bands of the pure components. Both vCs and vLi shift to higher energies with increasing mole fraction of CsCl and LiCl, respectively. The scattering intensity spectra of the mixtures are compared with the simulated additive spectra of the component salts. Increasing temperature increases drastically the isotropic intensity of the vLi band but has minor effects on the anisotropic intensities. The data are discussed and interpreted in terms of interaction-induced polarizability
fluctuations. Short range overlap interactions, mainly between Li1 and Cl2, and the ââsymmetryââ of the local structure around the anion determine the breathing-like fluctuations which contribute to isotropic scattering and account for the drastic temperature and composition dependence of the Raman intensities. The main contribution to anisotropic scattering arises from near-neighbor
dipole-induced-dipole interactions between the highly polarized Cs+ and Cl- ions.
Abstract: We have studied the reduction mechanism and electronic conduction during electrodeposition of tantalum in various TaCl5-alkali chloride melts at temperatures up to 1100 K. This has been performed by simultaneous measurements of impedance and Raman spectra together with cyclic voltammograms. A detailed analysis of electrochemical and spectroscopic results yields the following predominant reduction steps during electrodeposition in pure alkali chloride melts: Ta(V) -Ta(IV)-Ta(0). The equilibrium potentials of the corresponding redox reactions are separated by 40 mV which is clearly resolved in impedance measurements. In LiCl/KCl-eutectic melts a three step mechanism is found with Ta(III) being the intermediate species. In evaluating the impedance data we found indications for electronic contributions which are most prominent with added oxide impurities to the molten electrolyte. Direct evidence for an appreciable electronic conductivity has been obtained by electrochemical polarization measurements. These are reported here the first time for fused KCl-TaCl5/Ta at 1050 K, where electronic conductivities up to 0.5 Ohm(-1) cm(-1) have been measured, i.e. of same order of magnitude as ionic conductivities.
Abstract: Isotropic and anisotropic light scattering (Raman) spectra of molten LiF at 865 degrees C have been measured. The data are discussed in terms of the interaction-induced polarizability model and molecular dynamics simulations. The systematics of the reduced Raman spectra of the LiX (X = F, Cl, Br, I) melts are examined and an account of the differences is proposed in terms of the structural peculiarities of LiF
Abstract: The existence of stable glass-forming liquid mixtures in the RCl3-AlCl3 (R = Nd, Gd) binary systems is established. Based on Raman spectroscopic measurements, a structural is proposed for these glasses where the main participating units are 'AlCl4' and in part 'Al2Cl7'. The coordination of the lanthanide is nine-fold for neodymium and eight-fold for gadolinium.
Abstract: Raman spectra of the ''molecular'' polycrystalline solids HgCl2 (D2h16), HgBr2 (C2upsilon12) and of the yellow form of HgI2 (C2upsilon12) were measured from LN2 up to premelting temperatures. Polarized Raman spectra of molten HgX2 (X = Cl, Br, I) were measured at temperatures up to 950 K. The pure rotational band contour and the vibrational rotational contour of the HgX2 vapors were also measured. Upon melting the vibrational modes of the high temperature solid appear to be preserved. The spectra of the three liquids are similar and are best correlated to the spectra of the D2h16 (HgCl2) solid and the vibrational modes of the HgX2 molecules. Reduced Raman spectra of the liquids show splitting of the stretching mode to a doublet, nu1 (A1) and nu1 (B2g), which is attributed to strong intermolecular coupling. The nu2 and nu3 internal modes of the solid are also transferred into the melt. The predominant features of the low frequency reduced spectra is a band, nu(R), which is assigned to the rotatory modes of the HgX2 molecules and can be correlated to both the rotational band contour of the vapor and the librational modes of the solid. With increasing temperature the spectra of the liquid show softening of the rotatory modes and a blue shift of the nu1 mode, both implying weakening of the intermolecular coupling. An overall decrease in the Raman.
Abstract: Green platelike hexagonal crystals of CsV(SO4)2 were obtained by stepwise cooling in the range 500-400-degrees-C of solutions of V2O5 in Cs2S2O7, either under SO2(g) atmosphere or during catalytic conversion of SO2, in a 10% SO2, 11% O2, and 79% N2 gas mixture. The crystals belong to the trigonal system, space group P3BAR, with a = b = 4.868(1) A and c = 8.767(2) angstrom at 140 K and Z = 1. The phase represents a novel structure type with tetrahedral SO42- ions linked to octahedrally coordinated vanadium(III) in a way different from the known KV(SO4)2 and other related M(I)M(III)(SO4)2 Structures. The infrared and Raman spectra of powdered CsV(SO4)2 show close analogy to those of KV(SO4)2. The crystal Raman spectra show vibrational bands the polarization properties of which cannot be explained in terms of the crystallographic point group and a totally symmetric electronic ground state. Above 1300 cm-1 the Raman spectra, particularly at lower temperatures, show a coarse structure, which is interpreted as electronic Raman transitions between the spin-orbit split states of the A-3(g) and E-3(g) levels
Abstract: In situ surface enhanced Raman spectra (SERS) of adsorbed oxygen were obtained during oxygen adsorption and ethylene epoxidation on Ag catalyst surfaces at temperatures between 25 and 400-degrees-C and atmospheric total pressure. Three types of Ag catalysts were investigated: (I) Ag supported on alpha-Al2O3, (II) Ag films deposited on quartz and (III) Ag films deposited on the O2- Conducting solid electrolyte Y2O3-stabilized ZrO2 (YSZ). In the last case the effect of the application of external voltages (-2 V to +2 V) on the SERS was also examined ''in situ'' in order to investigate the effect of Non-Faradaic Electrochemical Modification of Catalytic Activity (NEMCA). Bands at 240, 345, 815, 870, 980 and 1630 cm-1 were observed for the oxygen-Ag/YSZ system. The 815 and 980 cm-1 bands were also observed for the Ag/quartz and Ag/alpha-Al2O3 Samples. The intense band at 815 cm-1, assigned to the O-O stretching vibration of a molecularly adsorbed oxygen species, exhibited an isotope shift of 20 cm-1 upon replacing O-16(2) with O-18(2). This band is present during ethylene epoxidation at temperatures up to 350-degrees-C and its relative Raman intensity decreases with decreasing O2 to C2H4 ratio. The excitation profile of the 815 cm-1 band and the existence of the overtone at 1630 cm-1 indicate that preresonance Raman enhancement is also responsible for the high intensity spectra obtained. In the case of Ag/YSZ it was found that increasing catalyst potential strengthens the O-O bond and increases the band intensity, while decreasing catalyst potential causes a decrease in bond strength and band intensity. These observations can be accounted for within the framework of previous NEMCA studies. However the change in relative band intensity can also be due to the effect of applied voltage and changing Fermi level and work function on the enhancing mechanism of SERS.
Abstract: Modulation and photon counting Raman spectroelectrochemical methods have been applied for studying amorphous carbon electrode surfaces during the electrolysis of HgCl2 in LiCl-KCl eutectic at 370-degrees-C. A new Raman band measured at 152 cm-1 was attributed to subvalent Hg2Cl2 species. The Raman signal arises from the melt solvent having appreciable Hg2Cl2 concentrations in the vicinity of the cathode.
Abstract: The vapors over solid gold(III) chloride and the vapor-phase equilibria of the gold(III) chloride-aluminum(III) chloride binary system have been investigated spectrophotometrically. The thermodynamic functions of the sublimation 2AuCl3(s) = Au2Cl6(g) were determined: DELTA-H(S)-degrees = 114.2 +/- 1.8 kJ mol and DELTA-S(S)-degrees = 160.5 +/- 3.3 J mol-1 K-1 (480 < T < 580K). One predominant vapor complex found in the binary system formed according to the reaction AuCl3(s) + 1/2Al2Cl6(g) = AuAlCl6(g) with DELTA-H(R)-degrees = 59.9 +/- 0.8 kJ mol-1 and DELTA-S(R)-degrees = 91.5 +/- 1.6 J mol-1 K-1 (470 < T < 550 K). At 470 K and 1 atm Al2Cl6(g) pressure the volatility enhancement of AuCl3 is approximately 300. The electronic absorption spectra of the Au2Cl6(g) and AuAlC16(g) molecules were interpreted in terms of a distorted square planar geometry of Au(III). "Bridged" and "terminal" ligand-to-metal charge-transfer bands were indentified in the spectra.
Abstract: Raman spectra of molten HgX2-Hg (X = Cl, Br, I) systems have been obtained at compositions up to 30 mol % in Hg from 550 to 818 K. The dissolution of mercury in mercury halides gives rise to resonance-enhanced Raman bands which were interpreted to account for Hg2X2 type molecular species formed in all mercury compositions and Hg3X2 type molecules formed at high mercury mole fractions. Spectra were also obtained from HgX2-HgX'2-Hg (X = F, Cl, Br, I) mixtures and were attributed to mixed mercury(I) (sub)halide molecules Hg2XX' formed in the melt. The Hg2X2 and Hg2XX' molecules possess a linear symmetry, and the Hg-Hg stretching frequencies for all 10 molecules were found to be between approximately 180 cm-1 (Hg2F2) and approximately 100 cm-1 (Hg2I2). A linear Hg3 chain is formed in thc Hg3X2 molecules bound to two terminal halides. The formation of Hg3 chains was further confirmed by the Raman spectra of Hg3(AlCl4)2 melts. It is suggested that in the melt mixtures intermolecular interactions between HgX2 and Hg2X2 molecules lead to an alteration of oxidation states which account for a "hopping" like conduction.
Abstract: Raman spectra of gold(III) chloride in the solid and vapor (AU2Cl6(g)) phases and of the vapor complex AuAlCl6(g) have been measured at temperatures up to 570 K. The distribution of vibrational modes in AuCl3(s) have been derived and six low frequency Raman bands have been assigned to librational modes of the solid. Fifteen internal modes of the AuCl3(s) have been measured in the Raman and IR spectra and were assigned to the AU2Cl6 molecule in the crystal. Normal coordinate analysis was performed and a complete force field was derived for the AU2Cl6 in the crystal. Experimental difficulties arising from laser induced decomposition of the colored vapors AU2Cl6 and AuAlCl6 were overcome by using a rotating Raman cell inside the optical furnace. Four polarized bands at 386, 324, 157 and 96 cm-1 and their combinations and overtones have been measured in the resonance Raman spectra of AU2Cl6(g). The Raman intensities of the AuAlCl6(g) were also resonance enhanced and seven polarized fundamentals have been measured at 495, 386, 330, 300, 183, 156 and 98 cm-1. A tentative normal coordinate analysis was performed for AU2Cl6(g) and AuAlCl6(g). The force field calculations of AuAlCl6(g) with a C2v symmetry were based on a procedure of mixing the force constants of the Al2Cl6(g) and Au2Cl6(g).
Abstract: We report spontaneous Brillouin and photon correlation spectroscopic results on the dynamics of the local density fluctuations in the ionic mixed salt xKNO3.yCa(NO3)2 with m olar ratios 2:1, 3:2, and 1:1. For these mixtures, the density relaxation function g(t) changes from a stretched exponential (beta = 0.47) near the glass transition temperature T(g), to an exponential (beta = 1) form at high temperatures, whereas the composition dependence of the relaxation time-tau-reflects mainly differences between the T(g) values. The 3:2 fragile glass (T(g) = 60-degrees-C) is one of the few examples where g(t) is now known from the glass-like (60-90-degrees-C) to the liquid-like (T > 100-degrees-C) region through the application of various dynamic scattering techniques. The tau-(T) and the evolution of the width beta of the distribution are discussed in terms of the physical pictures implied by current models of the liquid and glass transition phase.
Abstract: The density correlation function, C(t), in the mixed ionic glass KNO3.Ca(NO3)2 with three different compositions between 50 and 70% at temperatures near and above the glass transition, T(g), was measured by photon correlation spectroscopy. The C(t) which is of recent theoretical interest is well represented by the non-exponential form exp(-t/tau)beta with beta = 0.47 +/- 0.03 insensitive to temperature and composition variation in the investigated range. The relaxation time, tau, is independent of the wavevector, q, in the range (1.2-4.7) x 10(-3) angstrom -1 and its dependence on the composition arises mainly from the composition-dependent T(g). The relaxation time which is in agreement with recent neutron spin-echo (NSE) (time domain 2 x 10(-11)-2 x 10(-9) s) is associated with local rearrangements involving a few neighbouring ions. Information about local structure can be extracted from the low-frequency
Abstract: The phase diagram of the ScI3-CsI system has been determined and the existence of two solid compounds, Cs2ScI6 and Cs3Sc2I9, has been established. The Raman spectra of molten ScI3-CsI mixtures containing up to 60 mol % ScI3 have been measured at temperatures up to 700-degrees-C. The temperature dependence of the Raman spectra of polycrystalline Cs3ScI6 and Cs3Sc2I9 compounds from ambient temperatures to temperatures above melting have also been measured. The data are discussed in terms of the possible species formed in the melt mixtures. It is suggested that two predominant ionic species in equilibrium, ScI63- half-arrow-pointing-right-over-half-arrow-pointing-left ScI4- + 2I-, prevail in the melt. A third binuclear Sc species is also present at high ScI3 concentrations. The Raman frequencies attributed to the ionic species are as follows: for ScI63-, nu-1 = 119 +/- 1 cm-1, nu-2 = 67 +/- 2 cm-1 (nu-5 almost-equal-to 80 cm-1); for ScI4-, nu-1 = 129 +/- 1 cm-1, nu-2 = 37 +/- 3 cm-1, nu-4 = 54 +/- 3 cm-1. The Raman spectra of vapors over an equimolar ScI3-CsI mixture have been measured at 800-degrees-C, and the observed bands at 127 +/- 1 and 153 +/- 1 cm-1 were assigned to the nu-1 stretching frequencies of the ScI4 tetrahedra in the CsScI4(g) molecule and of the ScI3(g) molecule, respectively.
Abstract: The vapour phase above an equimolar NaI-ErI3 mixture has been studied by
Knudsen cell mass spectrometry. The presence of the complex molecule NaErI4 in
the equilibrium vapor has been established. There is also evidence for the existence
of the complex dimer Na2Er2I8, in small amounts. The main complexation reaction is
given by reaction Nai(g) + ErI3(g) = NaErI4(g) with ÎH = -244 +/- 12 kJ mol-'1 and ÎS = -163 +/- 12 J mol-1 K-1
at 890 K. For the complex dimerization reaction 2NaErI4(g) = Na2Er2I8(g) the corresponding enthalpy
and entropy changes are ÎH = -200 +/- 20 kJ mol-1 and ÎS = -187 +/- 17 J mol-1 K-1
at 890 K. The volatility enhancement of ErI3 due to the complexation has been
calculated to be approximately 21 at 900 K and 50 at 825 K.
Abstract: Blue crystals of the compound Na2VO(S04), suitable for X-ray structure determination have been obtained by dissolving V2OS
in molten Na2S207 at a temperature of 400 OC and bubbling a 10% so2-90% N2 gas mixture through the solution. In a few
hours, blue needle-shaped crystals precipitated. The uni ue crystal structure belongs to the orthorhombic system in space group
P2,2,2, (No. 19), with a = 6.303 ( I ) A, b = 6.803 (1) 1, c = 16.682 (2) A, and Z = 4. The structure consists of sodium ions
and a three-dimensional network of vanadyl ions (V02+), interlinked by two kinds of bridging sulfate ions. Sulfate coordinates
to the vanadium unidentately, forming a distorted V06 octahedron with one V-O bond length of 1.595 (2) A, four in-plane bonds
between 2.01 and 2.07 A, and one bond opposite to the short one, with a length of 2.150 (2) A. The 0-V-O angles are distorted
from 90' by less than 12O. The sulfate groups are slightly deformed and tilted, in such a way that the V-0-S bond angles are
around 130 f 3'. Short sodium-oxygen contacts (2.35-2.41 A) are encountered. Sulfate groups 1 and 2, respectively, contain
one (O(7)) and two (O(8) and O(9)) oxygen atoms, which are uniquely bound by short bonds to S(1) and S(2), respectively.
Infrared and Raman spectra of the compound have been recorded and interpreted.
Abstract: Raman spectroscopy is used to determine the stoichiometry and thermodynamics of gaseous reactions at high temperatures
under static equilibrium conditions. It is pointed out that the correct formalism for correlating relative Raman band intensities with equilibrium constants should include a temperature factor, which depends on the stoichiometric coefficients. The experimental procedures and sets of experiments required for establishing the stoichiometry and the ÎÎ and ÎΣ of gaseous reactions are described and their effectiveness is tested by applying the method to a known reaction, A22Br6(g) = 2AλBr3(g). Accurate relative Raman intensity measurements are used for investigating two vapor complexation reactions: (a) ZrBr4(g)+ nAl2Br6(g) = ZrAl2nBr(6n+4)(g) temperatures 570-860 K and pressures up to 5.5 atm. It is shown that the predominant vapor complex present has n = 0.5 (ZrAlBr4) and that the thermodynamic functions according to this reaction (n = 0.5)
can be measured from the Raman experiments as ÎÎ = -29.5 (+/-)1.4 kJ/mol, ÎS = -58.0 (+/-))2.0 J/(mol.K). (b) ZrCl4(g) + nAl2Cl6(g)+ ZrAl2nCl(6n+4)(g) at temperatures 500-800 K and pressures up to 10 atm. It is shown that two major vapor complexes are present with n = 0.5 (ZrAICl7) and n = 1 (ZrAl2Cl10). The thermodynamic functions according to the two reactions can be measured from the Raman spectral data as ÎHo = -41.8 f 0.7 kJ/mol, ÎSo = -70.8 f 1.0 J/(mol-K)
for n = 0.5 and ÎHo = -61.6 f 5.6 kJ/mol, ÎSo = -123.5 * 10.2 J/(mol-K) for n = 1. A new temperature-dependent Raman band observed at 246 cm-' in the ZrBr4(g) spectra is attributed to Fermi resonance between the v3-v4 combination
and the v1 fundamental.
Abstract: Raman spectroscopy is used to determine the stoichiometry and thermodynamics of gaseous reactions at high temperatures
under static equilibrium conditions. It is pointed out that the correct formalism for correlating relative Raman band intensities
with equilibrium constants should include a temperature factor, which depends on the stoichiometric coefficients. The
experimental procedures and sets of experiments required for establishing the stoichiometry and the ÎHο and ÎSo of gaseous
reactions are described and their effectiveness is tested by applying the method to a known reaction, Al2Br6(g) = 2AlBr3(g).
Accurate relative Raman intensity measurements are used for investigating two vapor complexation reactions: (a) ZrBr4(g)
+ nAl2Br6(g) = ZrAl2nBr6n+4(g) temperatures 570-860 K and pressures up to 5.5 atm. It is shown that the predominant
vapor complex present has n = 0.5 (ZrAlBr7) and that the thermodynamic functions according to this reaction (n = 0.5 )
can be measured from the Raman experiments as ÎHο = -29.5 +/-1.4 kJ/mol, ÎSo = -58.0 +/-2.0 J/(mol.K). (b) ZrCl4(g) + nAl2Cl6(g)+ ZrAl2nCl2n+4(ga)t, temperatures 500-800 K and pressures up to 10 atm. It is shown that two major vapor
complexes are present with n = 0.5 (ZrAICl7) and n = 1 (ZrA22Cl10). The thermodynamic functions according to the two
reactions can be measured from the Raman spectral data as ÎHo = -41.8 +/- 0.7 kJ/mol, ÎSo = -70.8 +/-1.0 J/(mol-K)
for n = 0.5 and ÎHo = -61.6 +/- 5.6 kJ/mol, ÎSo = -123.5 +/-10.2 J/(mol-K) for n = 1. A new temperature-dependent
Raman band observed at 246 cm-1 in the ZrBr4(g) spectra is attributed to Fermi resonance between the v3-v4 combination
and the v1 fundamental.
Abstract: The formation of low-valence crystalline vanadium compounds was studied in the V2O5-M2S2O7
(M = Na, K, Cs) unsupported melt systems in the temperature range 350-480°C during SO*
oxidation with unconverted 10% SO2, 11% O2 and 79% N2 as the feed gas. A gas-molten-salt
reactor system was built to provide the possibility of isolating the crystalline precipitates under
operating conditions at any temperature by filtering the catalyst melts. Both V(IV) and V(III)
crystalline compounds were formed under different process conditions. The V(IV) compounds
K4(VO)4(S04)5, Na2VO(SO4) and Cs2(VO)2(SO4)3 and the V(III) compounds KV(SO4)2
NaV(SO4)2 and CsV(SO4)2 were isolated from the melts. A drop in the catalytic activity was
observed at temperatures where these compounds started to precipitate. For the first time it has
been possible to observe the drop in catalytic activity and the formation of low-soluble vanadium
compounds simultaneous/y. It was also found that (i) high alkali-to-vandium ratios, large alkali
cation promoters, or mixing of the alkali promoters caused the precipitation and the steep activity
drop to occur at lower temperatures, and (ii) the crystalline precipitates of V(IV) and V(II1) could
be redissolved by a heat treatment at/or above 470°C or by purging the melts with N2. The thermal
stability of the V(IV) compounds has been investigated by means of DTA. Furthermore the decomposition
rate of KV(SO& and K4(V0)3(S04)5 during isothermal heating at different temperatures in
the range 470-510°C has been measured and IR spectra of the decomposition products have been
recorded and interpreted. The results indicate that a heat treatment of melts containing large
amounts of V(IV) and V(III) precipitates leads to reoxidation of vanadium to the +V oxidation
state. Certain conditions required for reactivation of deactivated catalysts are pointed out and are
discussed in relation to the dissolution of the precipitates in the melts.
Abstract: The formation of low-valence crystalline vanadium compounds was studied in the V2O5-M2S2O7,
(M = Na, K, Cs) unsupported melt systems in the temperature range 350-480°C during SO2
oxidation with unconverted 10% SO2, 11% O2 and 79% N2 as the feed gas. A gas-molten-salt
reactor system was built to provide the possibility of isolating the crystalline precipitates under
operating conditions at any temperature by filtering the catalyst melts. Both V(IV) and V(III)
crystalline compounds were formed under different process conditions. The V(IV) compounds
K4(VO)3S05, Na2VO(SO,4)2 and Cs2(VO)2(SO4)3 and the V(III) compounds KV(SO4)2,
NaV(SO4), and CsV(SO4)2 were isolated from the melts. A drop in the catalytic activity was
observed at temperatures where these compounds started to precipitate. For the first time it has
been possible to observe the drop in catalytic activity and the formation of low-soluble vanadium
compounds simultaneous/y. It was also found that (i) high alkali-to-vandium ratios, large alkali
cation promoters, or mixing of the alkali promoters caused the precipitation and the steep activity
drop to occur at lower temperatures, and (ii) the crystalline precipitates of V(IV) and V(II1) could
be redissolved by a heat treatment at/or above 470°C or by purging the melts with N2. The thermal
stability of the V(IV) compounds has been investigated by means of DTA. Furthermore the decomposition
rate of KV(SO& and K4(V0)3(S04)5 during isothermal heating at different temperatures in
the range 470-510°C has been measured and IR spectra of the decomposition products have been
recorded and interpreted. The results indicate that a heat treatment of melts containing large
amounts of V(IV) and V(II1) precipitates leads to reoxidation of vanadium to the +V oxidation
state. Certain conditions required for reactivation of deactivated catalysts are pointed out and are
discussed in relation to the dissolution of the precipitates in the melts. o 1989 Academic PRSS, hc.
Abstract: Raman spectra of iron(III) chloride vapors (Fe2Cl6(g) and FeCl3(g)) and of the vapor complex FeAlCl6(g) have been measured in the temperature range 500-900 K. Experimental difficulties arising from decomposition of the vapors by the laser lines used were solved by designing and using a rotating, fused silica cell, inside an optical furnace. The Fe2Cl6(g) dimer spectra were interpreted in terms of D2h molecular symmetry. The main features of the spectra are four resonance enhanced polarized bands at 422, 305, 150 and 78 cm-1 as well as four depolarized bands. All the observed Raman active dimer fundamentals were assigned and, in combination with literature data, were used for normal coordinate analysis calculations. The resonance-Raman spectra of the FeCl3(g) monomer were interpreted in terms of a D3h molecular symmetry. Three bands at 450,370 and 111 cm-1 were assigned to the v4,v1 and v3 Raman active fudamentals, respectively. A relatively strong polarized band at 231 cm-1 was assigned to the first overtone of the v2,IR-active fundamental of FeCl3(g). Raman spectra of the complex FeAlCl6(g) were measured in equilibrium with a mixture of Al2Cl6(g) and iron (III) chlorides vapors. Two relatively strong polarized bands at 413 and 88 cm-1 as well as four weak polarized and six depolarized bands, seen in the spectra of the vapor mixture, were attributed to the vapor complex. The spectra were interpreted in terms of a C2v symmetry for the FeAlCl6(g) molecule. Relative intensity measurements, carried out for both the iron(III) chloride vapors and the vapor mixture containing the complex, indicate that by increasing the laser frequency from red to blue, the spectroscopic temperature increases and the Fe2Cl6(g) and/or the FeAlCl6(g) molecules dissociate to form FeCl3(g). The vibrational frequencies, observed and assigned in this work were combined with literature data and were used to calculate the thermodynamic functions of Fe2Cl6(g), Al2Cl6(g) and FeAlCl6(g) molecules.
Abstract: Blue crystals of K,(VO)3(S04)5 suitable for X-ray structure determination have been obtained from solutions of V205 in molten
K2S207 under a SO2/N2 gas mixture. Lowering the temperature from the range 470-450 OC to the range 440-420 C causes
small crystals to precipitate after several hours. The compound crystallizes in the monoclinic space group P2,/n (No. 14) with
a = 8.746 (2) A, b = 16.142 (2) A, c = 14.416 (2) A, and β= 106.81 (1)' at 18 C and Z = 4. It contains three different distorted
V06 octahedra and five distorted SO4 tetrahedra. The central vanadium atoms have a short bond to one oxide ion, four longer
bonds to the oxygens of four sulfate groups, and an especially long axial bond to a fifth SO4 2-. The vanadium environment is
similar to what is found for other vanadyl compounds. The structure has five different sulfate groups, with three of the four sulfate
oxygens bridging the vanadiums in a complicated packing pattern. Principal component analyses were performed to examine
structure correlations among different sulfate and V06 groups. Infrared and Raman spectra of the compound have been recorded
and interpreted.
Abstract: Nornal coordinate analyses were performed for Fe2Cl6 and FeAlCl6 on the basis of new Raman data. Calculated mean amplitudes of vibration are reported.
Abstract: Green KV(S04)2 crystals were synthesized by dissolution of V205 in a KHS04 melt at 450 OC under SO2(g) atmosphere. Slow
cooling of the solution from 450 to 250 C in 3 weeks gave small crystals that were used for X-ray structure determination and
for obtaining oriented-cr stal Raman and infrared spectra. The crystal structure, in rhombohedral (trigonal) space group RJ
with a = b = 4.781 (1) A and c = 23.545 (5) A at ~130 C and Z = 3, consists of a unique arrangement of tetrahedral SO4 2-
linked to octahedrally coordinated vanadium(III). The structure is compared to other closely related M(I)M(III)(S04)2 structures.
Infrared spectra on powder and on crystals along c could be assigned conclusively. Raman spectra were measured from small
oriented single crystals by using different light polarizations. Anomalous polarization and preresonance enhancement of certain
Raman bands were observed. Ten Raman-active modes were predicted by group-theoretical analysis whereas the experiments
showed the presence of eleven bands. The extra band at - 1560 cm-1 was attributed to a d - d electronic Raman transition,
ve, 3Eg - Ag, of vanadium(III) in the trigonal crystal field.
Abstract: Raman and IR spectra were obtained of molten AlCl3NH3, AlCl3ND3 and
AlBr3NH3 in addition to chloroaluminate mixtures of the AlCl3NH3. The main spectral
features of the gaseous AlCl3NH3 molecules having a C3v symmetry are retained in the
molten and glassy states. Some additional bands were observed both in the pure liquid and
in mixtures with chloroaluminate melts. The spectra indicated that the dissociation reaction
2AlCl3NH3 = AlCl4- + [AlCl2(NH3)2]+ occurs with K ~3 x 10-3 (mole fraction basis).
Frequency shifts found on liquefaction demonstrate that extensive hydrogen bonding
takes place between AlCl3NH3 molecules. This observationis supported by the glass-forming
nature of AlCl3NH3. The molecule Al2Cl6NH3 seems to exist in binary AlCl3-AICl3NH3
melts.
Abstract: Raman spectra of vapor mixtures ZrCl4-POCl3, HfCl4-POCl3, ZrCl4-AlCl3 and
HfCl4--AlCl3 are obtained in the temperature range 3OO-500°C. The spectra consist of
superposition of bands due to the component gases plus a few new bands which were
attributed to vapor complexation. A comparison of the spectra features in the systems
MCl4-POCl3 (M = Zr or Hf) with the spectra of the 1: 1 liquid and glass MCI4 POCl3
(M = Zr or Hf) with the spectra of the 1: 1 liquid and glass MCl4- POC13 indicate that the
vapor complexes also have a 1: 1 stoichiometry and that complexing occurs through oxygen
bridging. The strongest Raman bands for the Zr-O-P and the Hf-O-P complex are at 508
and 512 cm-1, respectively. For the MCl.-AlC13 systems two possible vapor complexes,
MAl2Cl10 and MAlCl7, are considered. Temperature dependence measurements of the
Raman spectra of the ZrCl4-AlCl3 systems indicate that the predominant vapor complex
is probably 1 : 1 and permit the estimation of the enthalpy of the reaction:
ZrCl4(g)+0.5Al2C16(g) = ZrAlCl7(g) ; ÎH = -34.9 +/-2.5 kJ mol-1. The strongest Raman
bands for the Zr-Cl-Al and the Hf-Cl-Al complex are at 401 and 391 cn- 1, respectively,
and is assigned to M-Cl (terminal) stretching.
Abstract: Crystalline NbAlCI8 was prepared as a new type of dinuclear halide complex by the direct reaction of Al2Cl6 with Nb2Cl10
at ~200 âC in evacuated sealed glass ampoules. The yellow compound is orthorhombic, space group Cmcm, with a =
8.016 (2) A, b = 17.139 (4) A, c = 8.1 16 (2) A, V = 111 5.1 A3, D meas=d 2.40 (2) gcm-3 and Dcalcd= 2.403 gcm-3 for
Z = 4. The crystal and molecular structure determination was based on three-dimensional X-ray diffractometer data refined
to a final conventional R factor of 0.030 for 639 independent reflections with I >2 Ï(Î). The crystals contain dinuclear
Cl4NbCI2AlCl2 molecules with mm symmetry, consisting of an AlCI4 tetrahedron sharing a common edge with a distorted
NbCI6 octahedron. AI-Cl bond lengths of 2.078 (2) and 2.200 (2) 8, and Nb-Cl bond lengths of 2.219 (1). 2.288 (1),
and 2.643 (1) 8, were observed. The Nb-Cl bridge bonds are longer than in the Nb2Cl10 molecule, thus indicating a higher
Lewis acidity of AICl3 compared to that of NbCl5. Polarized Raman spectra of NbAlCl8 single crystals were obtained
at room temperature. The factor-group analysis of vibrations in crystalline NbAlCl8 was used for the assignment of the
observed Raman bands. Raman spectra of melt mixtures of NbCI5 with AlCl3 at 235 C were characterized by a superposition
of bands due to Al2Cl6(l), Nb2Cl10(l), and NbCI5(l), together with NbAlCl8(l). Measurements of relative Raman band
intensities in the mixtures showed two strongly polarized bands at 416 and 364 cm-1 and other weaker bands due to NbAlCl8
complexes present in the melts. Raman spectra of vapors over the liquid mixtures at temperatures between 235 and 350
C were mainly due to Al2Cl6(g) and NbCl5(g) molecules. Two new polarized bands observed in the spectra at 418 and
369 cm-1 were attributed to the formation of the NbAlCl8 gaseous molecule.
Abstract: Molten eutectic mixtures of KI-LiI and CsCl-LiCl at 300-400 âC were equilibrated with I2 vapor or I2-ICl
vapor at pressures of 0.002-2 atm and were investigated by means of Raman and visible-UV spectroscopy.
The observed polarized Raman bands were attributed to the symmetric stretching vibrations of I3- (112 cm-1),
I2Cl- (184 cm-1), and ICl2- (271 cm-1). Further evidence for the presence of these trihalide anions in the melts
was given by the visible-UV spectra. A band at 161 cm-1 in the Raman spectrum of the I2/KI-LiI melt was
attributed to a polyiodide of higher molecular weight than the triodide. There is evidence for the disproportionation
of I2Cl- in the I2/CsCl-LiCl melt.
Abstract: Raman spectra of gaseous NH3:AlCl3 and NH3:AlBr3 were recorded at 400 °C. The observed Raman frequencies in combination with reported infrared frequencies for NH3:AlCl3 and ab initio molecular orbital calculations on NH3:AlCl3 and NH3:AlF3 were used to derive force constants for all three NH3:AlX3 complexes (X=F, Cl, Br) based on an adjusted valence force field (AVFF) concept. The resulting force constant calculations produced complete sets of A1 and E mode frequencies for each complex. Statistical mechanical analyses were then performed using the A1 and E mode frequencies together with estimated values for the torsional mode of each complex and published enthalpy data. From these analyses, the relative thermodynamic stability of each complex was determined. At 700 and 1000 K, NH3:AlCl3 was found to be more stable than NH3:AlBr3. It was further predicted that the reaction of gaseous NH3 with solid AlF3 to form NH3:AlF3 is not favored in this temperature range, which provides an explanation for the lack of success in prior efforts to produce NH3:AlF3.
Abstract: The infrared spectra of aluminium chloride vapour (Al2Cl6 and AlCl3) including Cl35 and Cl37 isotopes at 473-843 K were measured in the region 700-50 cm-1 with an evacuable Fourier transform spectrometer by transmission and emission techniques. Evacuable cells of nickel were employed having windows of type IIa diamond and sealed with gold O-rings. Raman spectra of Al2Cl6 vapour at ca 500 K and of AlCl3 at 1075 K with pressures from 0.3 to 10 atm were recorded, polarization measurements were carried out and additional spectra of the 35Cl and 37Cl compounds were obtained. The dimer spectra were interpreted in terms of D2h symmetry. All the nine Raman-active and seven of the infrared-active dimer fundamentals were assigned. The IR active mode v10(B1u), expected below 40 cm-1, and the inactive mode v5(Au) were left unassigned. The monomer spectra were interpreted in terms of D3h symmetry and all four fundamentals were assigned. A dimer force field, involving 12 independent force constants, was derived. The calculated frequencies were fitted with a least-squares programme to 30 observed fundamentals of Al2 35Cl6 and Al2 37Cl6 and 14 additional isotopic shifts transferred from previous matrix isolation spectra. A complete force field for the monomer was derived, using the four observed fundamentals and seven isotopic shifts transferred from previously reported matrix isolation spectra.
Abstract: The blue solutions produced by reaction between aluminum and sulfur in basic CsCl-AICl, melts have been examined
by means of Raman spectroscopic, spectrophotometric, and ESR measurements and are mainly attributed to the presence
of S; species. The formal absorptivity of the blue solutions, with an absorption maximum near 16 700 cm-', was measured
in the temperature range 390-470 OC and at different sulfur to aluminum formality ratios. The Raman intensity of the
v, = 529 cm-' stretching mode was also measured at different sulfur to aluminum formality ratios and in conjunction with
the absorption measurements was used to determine the possible number of species formed. The findings have been best
interpreted by an equilibrium between the blue S3- entity, S(-II) species (present in polymeric chain species of the [AlSCl2]n n-
type), and molecular sulfur. No direct evidence for the formation of other sulfur species has been found, but there are
indirect indications of a possible existence of other sulfur species. ESR measurements show the presence of the paramagnetic
S3- radical with g = 2.023 and a hyperfine splitting into six lines arising from a direct coupling of the S3- with the aluminum
atom ( I = 5 / 2 ) . The data are discussed in terms of the possible formation of [S3AlCl3]- and [S3AlCl4]2- species in these
melts. Finally a single-line ESR spectrum of blue sulfur species in LiCI-CsC1 eutectic was attributed to the presence of
S3- with g = 2.028. This "free" radical had its stretching mode at 527 cm-I.
Abstract: Raman spectra of vapor-phase compounds CuFeCl5, HfCl4â¢POC13 and NH3â¢AIX3 (Χ = Cl, Br) have been measured at ~500-1000 Î. Resonance Raman spectra obtained from an equilibrium vapor mixture containing CuFeCl5(g) showed two characteristic polarized bands at 441 and 275 cm-1⢠which were attributed to trigonally coordinated cu(rr) and suggested a C2v symmetry for the vapor complex. Raman spectra of HfCl4-POCl3 vapors were characterized by a superposition of (1) strong bands due to POCl3(g) and HfCl4(g) and (2) a few new bands (at 512, 1221, and 1263 cm-1) due to the vapor complex. Î comparison of the vapor-complex spectra with those of HfCl4(g) and POCl3(g) as well as HfCl4'POCl3 in the liquid
and glass states indicated that the bonding of the complex with a C3v symmetry occurs through an oxygen bridge. Raman spectra of the vapors over liquid NH4AlX4 (Χ = Cl, Br) were measured and compared with the spectra of the liquid NH4AlX4 itself as well as NH3AICl3 in the vapor and liquid states. The measurements support the view that dissociative vaporization and further dissociation occur according to the reaction :
NH4AlX4(l) = NH3AlX3(g) + HX(g) = NH3(g) + AlX3(g) + HX(g)
For NH3AICl3, the C3v molecular symmetry of the gaseous state is not preserved in the liquid state whose structure appears to be network-like.
Abstract: The energies of combustion of Sb(c) and Sb2S3(c) in fluorine were measund in a bomb calorimeter. The standard enthalpies of formation DHfi(298.15 K), of SbF5 (l) and Sb2S3(c) were derived to be -(1327.95+/-0.93) kJ mol-1 and -(141.8 +/-4.1) kJ mol-1, respectively. High temperatureenthalpy increments were determined for crystalline and liquid Sb2S3 by drop calorimetry. The enthalpy and entropy of melting of Sb2S3(c) at 823 K were derived to be
(40.64 +/- 0.20) kJ mol-1 and (49.38 +/- 0.24) J K-1 mol-1, respectively.
Abstract: Raman spectra were obtained at temperatures up to 1200 K for vapors over liquid indium halides with In:X (X=Cl, Br) ratios of 1:1, 1:2, and 1:3 and for vapors over liquid InAlX4. Spectra were also measured for molten InX2 and InAlX4 salts. The spectra of InX vapors consisted of O, Q, and S vibrationalârotational contours with maxima at Q(InCl) =305 cmâ1 and Q(InBr) =213 cmâ1. Pure rotational O and S band contours were also resolved at frequencies close to the frequency of the laser excitation line. Vibrationalârotational contours for the InX molecules were simulated using known molecular constants and accounting for contributions of both trace and anisotropic scattering. Preresonance enhancement of the Raman intensities and changes in the ''linear'' depolarization ratio with laser frequency were also observed for the InX molecules. The spectra of vapors over InX3 were characteristic of a dimerâmonomer indium (III) halide equilibrium. Raman spectra of vapors over InX2 and InAlX4 liquids show the formation of vapor complexes and vapor dissociation according to the reactions: A comparison of the Raman spectra of liquid InX2 and InAlX4 with the corresponding spectra of the vapors indicates that the same molecular species are present in both phases.
Abstract: Laser excitation of equihbrium vapor mixtures ErCl3(s)-ACl3(g) (A = Al, Ga, In) at 475-1100 K gives rise both to resonance fluorescence from the f -f Er(III) transitions of the Er-Cl-A vapor complexes, and to Raman scattering due to the
vibrational modes of the ACl3 vapor. The laser-induced fluorescence from the 4F9/2, 4S 3/2 and 2H11/2 states has been investigated at different temperatures and excitation.
Abstract: The energies of combusion of β-As4S4 and vitreous As2S3 in fluorine were measured in a bomb calorimeter. High-temperature enthalpy increments were also determined by drop calorimetry. The standard enthalpies of formation ÎHfo(298.15 K), were found to be â(134.6±6.7) kJ molâ1 and â(69.6 ± 4.2) kJ molâ1 for β-As4S4 and vitreous As2S3, respectively. Based on the measured results and data from the literature, the thermodynamic properties of the minerals realgar, α-As4S4, and orpiment, As2S3(c) were derived. For realgar at 298.15 K, ÎHfo = â(138.1 ± 6.7) kJ molâ1, ÎSfo = â(22.3 ± 3.1) J Kâ1 molâ1, and ÎGfo = â(131.5 ± 6.8) kJ molâ1 are recommended and, for orpiment at 298.15 K, ÎHfo = â(91.6 ± 4.8) kJ molâ1, ÎSfo = â(3.1 ± 4.3) J Kâ1 molâ1, and ÎGfo = â(90.7 ± 5.0) kJ molâ1.
Abstract: The electronic absorption spectra of vapor-phase compounds formed by reacting SmCI3(s) and SmCl2(s) with gaseous AI2Cl6
have been measured at temperatures up to 800 K and total pressures up to 13 atm. The spectra of the pale yellow Sm(III)-AI-Cl
gaseous complex(es) were characteristic of the f - f electronic transitions of Sm(III). The spectra of the red-brown Sm(II)-AI-Cl
gaseous complex(es) showed high-intensity, broad bands which are attributed to 4f - 5d transitions of Sm(II). Spectrophotometric
measurements have been used to investigate the partial pressures of the vapor complexes at different Al2C16
pressures. Thermodynamic considerations suggest that the SmAl3CI12 is the predominant vapor species formed by the trivalent
samarium. For the reaction SmCl3(s) + 3/2Al2Cl6(g) = SmAl3Cl12(g) the values of ÎH = 6.7 kcal mol and ÎS = -1.0 eu
have been halogenated and vapor transported using A12Cl6 or A12Br6. A new method for the preparation of anhydrous
rare earth halide crystals is suggested. The data are discussed in terms of the systematics of formation and structure of
gaseous lanthanide chloride complexes.
Abstract: The vapor-phase equilibria of the cohalt(I1) chloride-indium(II1) chloride system have been investigatedspectrophotometrically in the temperature range from 900 to 1100 K and at total pressures from ~0.5 to ~4.0 atm. Thermodynamic considerations imply the reaction CoCl2(s) + 2InCl3(g) = CoIn2Cl8(g) [ÎH = -19.2 kcal/mol; ÎS = -24.0 cal/(mol deg)]. Increasing the temperature and/or decreasing the indium chloride pressure tends to dissociate the blue CoIn2Cl8 complex according to the reaction CoIn2Cl8(g) = InCl3(g) + CoInCl5(g) [ÎH= 34.4 kcal/mol; ÎS = 33.4 cal/(mol deg)]. The values of the thermodynamic functions relevarit to the formation of CoIn2Cl8 are compared with those of other cobalt chloride vapor complexes and are interpreted m indicating
similarities in the vapor structures.
Abstract: Resonance Raman spectra of vapor molecules formed by reacting gaseous aluminum chloride with solid PdCl2 and CuCl2 have been measured in the temperature range from 500 to 900 K and at total pressures up to 30 atm. The main features of the Raman spectra of the PdâAlâCl gaseous molecule are three polarized bands at 298, 176, and 84.5 cmâ1. The excitation profiles of these bands exhibit minima in the vicinity of the maximum Pd(II) ligand field absorption, thus suggesting the presence of a center of symmetry in the molecule. A D2h molecular symmetry is proposed for the PdAl2Cl8 vapor complex having Pd(II) as a central atom in square planar coordination. The Raman spectra of the CuâAlâCl vapors are interpreted to account for two different molecular species. Three polarized bands at 281, 174.5, and 84.5 cmâ1 are assigned to preresonance enhanced A1 fundamentals of the CuAl2Cl8 molecule. Two strong bands at 448 and 291.5 cmâ1 and their combinations and ovetones are assigned to resonance enhanced A1 fundamentals of the CuAlCl5 molecule having the Cu(II) in a trigonal coordination. Raman band intensity measurements using different laser line intensities suggest an increasing spectroscopic temperature and decomposition of the complex: CuAl2Cl8(g) = CuAlCl5(g)+AlCl3(g).
Abstract: Raman spectra of vapors over arsenic oxide have been obtained at temperature up to 1200 K. Three Raman bands not reported previously have been observed and vibrationalârotational contours for E and F species fundamentals of As4O6 have been resolved. A band of medium intensity at 410 cmâ1 was found to be polarized and its relatively high intensity was attributed to Fermi resonance between the 2 v6 and the v2 modes. A valence force field calculation has been carried out, and the mean amplitudes of vibration and Cartesian displacements of As4O6 have been evaluated. The vibrations have been compared with AsO3 fundamentals by a group theoretical correlation method.
Abstract: The reaction of solid palladium(II) bromide with gaseous aluminum(III) bromide to form a ceramic-red vapor complex has been investigated by spectrophotometry and by Raman spectroscopy at temperatures ranging from 550 to 900 K andtotal pressures up to -2 atm. The electronic absorption spectra of the complexes show an intense d - d band at - 1.96 μm-1and a charge-transfer band at -3.55 μm-1. The spectrophotometric data led to the conclusion that one predominant complex exists in the vapor formed by the reaction PdBr2(s) + Al2Br(g) = PdAl2Br8(g) with AN = 8.27 kcal/mol and AS = 8.04 eu. Raman spectra of the equilibrium vapor mixtures PdAl2Br8-Al2Br6-AlBr3 and Al2Br6-AlBr3 here obtained at different temperatures. The main features of the Raman spectra of the PdAl2Br8 gaseous molecule are three polarized bands at 180, 114, and -50 cm-1 . The excitation profiles of the5e bands exhibit minima in the vicinitS of the maximum Pd(II) d --d absorption. The electronic absorption and Raman spectra of the complex were interpreted in terms of a D2h symmetry for the vapor complex PdAl2Br8, where Pd(II) is in a square-planar coordination.
Abstract: Polarized spectra of evaporated thin films of As2S3 glass have been recorded before and after annealing at the glass transition temperature and compared with the corresponding spectrum of the bulk glass. The spectra of virgin films consist of several sharp molecular bands superposed on a networklike continuum which is characteristic of the bulk glass, whereas annealed films yield only the bulk glass spectrum albeit with some indication of residual nonstoichiometry. These results are direct evidence that irreversible thermostructural transformations (or equivalent photostructural transformations) in evaporated As2S3 films proceed through polymerization of a metastable molecular glass as suggested by deNeufville, Moss, and Ovshinsky. The polarized Raman spectra of the vapors over As2S3 liquid have been obtained and indicate the presence of serveral gaseous molecular species. The molecular constituency of the evaporated amorphous film is also complex but distinct from that of the vapor, an indication that deposition itself introduces some structural alterations.
Abstract: The Raman spectra of molten YCl3âA Cl (A=Cs, K, Li) mixtures have been measured at different compositions and temperatures up to 890 °C. The Raman spectra of polycrystalline Cs2NaYCl6 and YCl3 were also measured from 25 °C to temperatures above melting. The factor group analysis of crystalline Cs2NaYCl6 was used to identify the three Raman active modes (v1, v2, v5) of the YCl6 3- octahedra. For liquid mixtures rich in alkali halide, the predominant features of the spectra are characterized by a polarized and a depolarized band with frequencies near the v1 and v5 frequencies of the YCl6 3- octahedron and thus indicates the existence of such species in the melt. In melts containing above 25% YCl3 a new polarized band D appears in the spectra which shifts continuously and rapidly to higher energies with increasing YCl3 concentration. The frequency shift is attributed to a continuous distortion mechanism of the YCl6 3- octahedra by the neighboring yttrium ions. The continuous frequency shift of the D band and a comparison of the liquid and solid Raman spectra of yttrium chloride suggest the existence of lattice-type modes in these melts.
Abstract: The reaction of solid cobalt(II) bromide with gaseous aluminum bromide to form deep green gaseous complex(es) has been investigated spectrophotometrically in the range 550-900 K and at pressures up to 2 atm. Thermodynamic considerations suggest the reaction CoBr2(s) + Al2Cl6(g) = CoAl2Br8(g) [AH = 9.9 kcal/mol; AS = 9.4 eu]. The electronic absorption spectra are discussed in terms of the possible coordination of Co(II) in the gaseous molecule(s). Spectroscopic and thermodynamic considerations suggest that the predominant absorbing species in the gas phase is Co(AlBr4)2 molecules having the Co(II) in a close-to-octahedral coordination. The volatility enhancement ratios of cobalt(II) halide in the presence of various âacidicâ A2X6 gases are calculated and compared. At temperatures below 750 K, aluminum bromide is a better
gas-complexing agent than aluminum chloride for the respective cobalt halides.
Abstract: Raman, depolarization, and infrared spectra of the glass, liquid, and gaseous disordered phases of As2O3 have been studied at temperatures between 4.5 and 1200 K. Spectra recorded at temperatures in the range of the glass-liquid transition indicate that the microstructures of the glass and liquid are quite similar near Tg and can best be characterized as distorted layerlike remnants of the monoclinic crystalline phase, claudetite. Our results have been contrasted to corresponding results for As2S3 and As2Se3 and have been compared with the predictions of current models of the structure of As2X3-type glasses. The observed spectra are most compatible with the composite model which combines aspects of the layer and molecular models. No evidence is found to support the conjecture of Taylor, Bishop, and Mitchell that for layer-type As2X3 glasses a characteristic temperature Ts exists such that Ts>Tg and the layers catastrophically disintegrate at temperatures T>Ts. The temperature dependence of the Raman shift, full width at half-maximum (Î1 / 2), and integrated intensity of the 376-cm-1 band associated with the symmetric stretching mode of the As-O-As linkage have been studied as have the shifts with temperature of other prominent spectral features. We find that the glass transition temperature can be accurately determined from a plot of lnÎ1 / 2 vs ln(1000 / T) and that above Tg Î1 / 2(376 cm-1)âT1 / 2. The temperature dependence of the ν1 and ν3 modes of the AsO3 pyramidal unit indicates that the apex angle decreases with increasing temperature. The low-frequency (8-30 cm-1) region of the Raman spectrum of vitreous As2O3 has been carefully studied at 11.4 K. From the reduced Raman spectrum of the low-frequency region it is found that the product of the frequency-dependent coupling coefficient C(Ï) and the density of vibrational states g(Ï) varies as Ï2.5.
Abstract: Infrared absorption and polarized Raman spectra of monoclinic As2O3 and the room temperature Raman spectrum of cubic As2O3 have been recorded. A number of vibrational features possessed by the crystalline modifications of arsenic trioxide are common to crystals of As2S3 and As2Se3, but have been resolved in greater detail. In particular, the layered monoclinic phase, claudetite, exhibited rigid layer modes at Raman shifts of 30, 38, and 49 cm-1, and numerous Davydov doublets, all of which appeared as a consequence of weak layer-layer coupling. Oriented samples of claudetite yielded polarized Raman measurements which did not obey the symmetry-determined selection rules of the C2h5-P21 / n space group for reasons which can be traced to the fact that claudetite is biaxial. However, the vibrational frequencies of claudetite scale consistently to those of monoclinic As2S3 and As2Se3 by scaling factors of 0.82 and 0.58, respectively. Thus, many claudetite lines are related by the empirical scaling result to As2S3 modes belonging to vibrational species which have been identified by infrared reflectivity measurements. Recurring bands in the ordered and disordered phases of As2O3 are noted and structural similarities between the different phases are evidenced by vibrational features that are comparable in frequency and symmetry. Accordingly, layered structure in arsenic trioxide glass is inferred.
Abstract: The reaction of solid cobalt(II) chloride with gaseous aluminum chloride to form blue gaseous complex(es) has been studied spectrophotometrically, in the range 600-800 K and 1-3 atm. The data are rationalized in terms of the reaction: CoCl2(s) + Al2Cl6(g) CoAl2Cl8(g) (ÎH° = 10.0 ± 0.2 Kcal/mole, ÎS° = 9.8 ± 0.3 e.u.). The electronic absorption spectrum of the gaseous complex was compared with the spectra of Co(II) in different molten salt solvents. Thermodynamic and spectroscopic considerations suggest that the predominant absorbing species in the gaseous phase are Co(AlCl4)2 molecules having the Co(II) in a close to octahedral coordination.
Translated Abstract
Spektren und Thermodynamic der Kobalt(II)-chlorid - Aluminiumchlorid-Gaskomplexe
Die Reaktion von festem Kobalt(II)-chlorid mit gasförmigem Aluminiumchlorid unter Bildung blauer Gaskomplexe wurde spektralphotometrisch bei 600-800 K und 1-3 atm untersucht. Die erhaltenen Daten sind erklärbar mit der Reaktion: CoCl2(s) + Al2Cl6(g) CoAl2Cl8(g) (H° = 10,0 ± 0,2 Kcal/Mol), S° = 9,8 ± 0,3 Entropieeinheiten. Das Absorptionsspektrum des Gaskomplexes wurde mit den Spektren des CoII in Lösungen verschiedener geschmolzener Salze verglichen. Thermodynamische und spektroskopische Ãberlegungen legen die Annahme nahe, daà die vorherrschenden absorbierenden Spezies in der Gasphase Co(AlCl4)2-Molekeln mit CoII in oktaedrischer Koordination sind.
Abstract: The positions and polarization properties of seven bands observed in the
low temperature Raman and depolarization spectra of vitreous As2 03 are
successfully calculated using a modified molecular model. Nonnegligible
intermolecular coupling must be invoked to account for the other two
observed Raman bands.
Abstract: The molar enthalpies of mixing (ÎHm) in the liquid alkali chloride-cerium chloride mixtures have been measured at 845â. All the interaction parameters (λm= ÎHm / XlX2) are negative, increasing sharply from about -1 kcal/mol in LiCl-CeCl3 to about -25 kcal/mol in CsCl-CeCl3. The systems also have significant
energetic asymmetries with more negative values of Hm in the alkali chloride-rich than in thecerium chloride-rich regions. The results are discussed with respect to the following points: (1) comparison with the Davis conformal solution theory for the enthalpies of mixing of charge unsymmetrical fused salt mixtures; (2) âcomplexingâ in the mixture.
Abstract: The thermodynamic quantities of mixing in the liquid LaCl3-ACl (A = Li, Na, K, Rb, or Cs) mixtures have been measured. The integral enthalpies of mixing (ÎHm) for all the above binaries and the partial enthalpies of mixing in the LaCl3-KCl system have been determined calorimetrically. The partial Gibbs energies of mixing (A not Cs) have been determined by emf measurements. Two graphite-chlorine (C(s)lCl2(g)) electrodes were used in a galvanic cell of the type: C(s), Cl2(g)IACl(l)/alkali glass1 LaCl3(l)-ACl(l) 1 Cl2(g), C(s). The data are discussed with respect to the following points: (1) comparison with conformal solution theory for the enthalpies of mixing of charge unsymmetrical fused salt mixtures, and (2) âcomplexingâ in the mixture. The thermodynamic data indicate tendencies for âcomplexâ formation in the mixtures of Lacl3 with CsC1, RbCl, and KCl, while for the mixtures with NaCl and LiCl the Temkin model is applicable.
Abstract: The enthalpies of solution of the CsnMCI(n+2) [n = 1, 2, 3], MCI2 and CsCI solids in LiCI-KCI eutectic have been measured calorimetrically. From these measurements the enthalpies of formation of the complex solid compounds from the individual salts according to the reaction
n CsCI(s)+ MCI2(s) = CsnMCl(n+2) (s)[n = 1,2, 3]
were determined. The data are discussed in terms of the influence of the d electron crystal field splitting on the thermodynamic stability of these complex solids. It is concluded that the octahedral site stabilization energies of the M 2+ cations alone can provide a good approximation to the relative enthalpies of these reactions. Furthermore, a combination of the present data with our previous dataon the liquid enthalpies of mixing of the MC2(l)-CsCl(I) binaries permits an estimation of the enthalpies of fusion of the CsnMCI(n+2) compounds. Finally, by comparing the relative enthalpies of the above reaction with the relative enthalpies of fusion we concluded that the coordination of M(II) in fused MCI2 and in all fused CsnMCI(n+2) compounds is tetrahedral.
Abstract: The optical electronic absorption spectra of Pt(II) centers have been measured in liquid CsCl, KCl, LiCl, and CsCl---LiCl and KCl---LiCl mixtures over substantial temperature ranges. In CsCl at 650°â700°C and the eutectic mixtures below about 400°C the spectrum is that expected for normal square-planar PtCl4 2â complex anions at elevated temperatures. In LiCl and the mixed solvents at elevated temperatures the spectrum is modified by a drawing together of the two spin-allowed bands. This effect is attributed to the polarization of PtCl42â by the outer shell of Li+ ions.
Abstract: The enthalpies of mixing (Hm) of the following binary fused-salt mixtures have been determined calorimetrically: ZnCl2-CsCl, ZnCl2-LiCl, ZnCl2-AgCl, ZnBr2-CsBr, ZnBr2-LiBr at 665°C; ZnCl2-CsCl, ZnCl2-AgCl, and ZnCl2-ZnBr2 at 495°C. The results are discussed with respect to the following points: (1) Comparison with the transition metal chloride-alkali chloride systems, (2) complexing in the mixture. (3) effect of the network-like structure of pure ZnX2, and (4) effect of temperature.
Mischungsenthalpien der ladungsunsymmetrischen binären geschmolzenen Salzsysteme: ZnX2-AX (A = Li, Cs, Ag; X = Cl, Br)
Die Mischungsenthalpien (Hm) der folgenden binären Salzschmelzen wurden kalorimetrisch bestimmt: ZnCl2-CsCl, ZnCl2-LiCl, ZnCl2-AgCl, ZnBr2-CsBrLiBr bei 665°C; ZnCl2-CsCl, ZnCl2-AgCl und ZnCl2-ZnBr2 bei 495°C. Die Ergebnisse werden im Hinblick auf folgende Punkte diskutiert: 1. Vergleich mit Ãbergangsmetallchlorid-Alkalichlorid-Systemen, 2. Komplexbildung in der Mischung, 3. Einfluà der netzwerkähnlichen Struktur des reinen ZnX2 und 4. Einfluà der Temperatur.
Abstract: The reaction of solid cluster platinum(I1) chloride (Pt6Cl12) with gaseous aluminum chloride to form a purple gaseous complex has been studied spectrophotometrically. Thermodynamic considerations suggest the stoichiometry for the reaction:
1/6 Pt6Cl12(s) + Al2Cl6(g) = PtAl2Cl8(g) (ÎHr = 7.8 kcal/mol, ÎSr = 6.4 eu). The visible electronic absorption spectrum of the gaseous complex was compared with the spectrum of Pt(II) centers in liquid LiCl and interpreted in terms of a
square-planar PtCl4group sharing edges with two tetrachloroaluminates.
Abstract: The reaction of solid a-PdCl2 with gaseous Al2Cl6 to form a deep red gaseous complex has been studied spectrophotometrically. Thermodynamic considerations suggested the stoichiometry for the reaction
PdCl2(s) + Al2Cl6(g) = Pd(AlCl4)2(g): ÎH= 7 2 kcal/mol, ÎS= 9.45 eu. The visible and uv electronic absorption spectrum of the PdAl2Cl8 complex was interpreted in terms of a square-planar PdCl4 sharing edges with two tetrachloroaluminates. The data for the above reaction were compared wlth the data available in the literature for the corresponding reaction of NiCl2. The electronic absorption spectrum of NlAl2Cl8(g) is reported and interpreted as a NiCl6 octahedron sharing faces with two tetrachloroaluminates
Abstract: The enthalpies of mixing of MnCl2, FeCl2 and CoCl2 with the alkali chlorides have been measured at 810°C (all systems) and at 690°C (MnCl2---LiCl, FeCl2---LiCl, MnCl2---CsCl and FeCl2---CsCl only). The results are compared with similar data recently reported by the authors for the NiCl2-alkali chloride systems, and discussed with respect to the following points; (1) comparison with the theory of Davis; (2) âcomplexingâ in the mixture; (3) effect of d electrons; (4) effect of possible covalent and covalent-bridging interactions; and (5) effect of temperature. In a few systems partial enthalpy data are calculated and compared with corresponding excess free energy data. This gives some insight with respect to the excess entropy of mixing.
Abstract: The enthalpies of mixing (ÎHm) of nickel(II) chloride-alkali chloride mixtures have been measured at 810°C for liquid compositions up to 50 ,ole per cent NiCl2. The measurements consist of solid-liquid mixing data and of dilution measurements in which liquid mixtures containing 50 mole percent NiCl2 were diluted with pure liquid alkali chloride. The behavior of the enthalpy interaction parameters is discussed in terms of the probable formation of tetrahedral NiCl4staggered|2â configurations for mixtures containing KCl, RbCl and CsCl. A comparison with the corresponding MgCl2-systems suggests that the Ni2+ ion is probably tetrahedrally coordinated also in pure, liquid undercooled NiCl2 at 810°C.
Abstract: The integral enthalpies of mixing of the following binary fused-salt mixtures have been determined calorimetrically: (a) MnCl2-FeCl2, MnCl2-CoCl2, FeCl2-CoCl2 at 810°C; MnCl2-CdCl2, FeCl2-CdCl2 at 690°C; (b) CaCl2-MjCl2; and (c) MgCl2-MjCl2 with Mj = Mn, Fe, Co, at 810°C. The results are discussed with respect to the following points: (1) comparison with the binary alkaline-earth chloride systems; (2) comparison with the existing theories for the enthalpies of mixing of fused salts; and (3) effect of possible covalent or covalent-bridging interactions between the ions in the pure components and in the mixture. The results are interpreted in terms of a cyclic process which allows a separation of the enthalpy of mixing into two principal parts. One part is negative and is associated with ionic and dispersion interactions, as in the binary alkali halides and in some of the binary alkaline-earth chlorides. The other part is positive and is attributed to the effect of covalent interactions between the ions on the enthalpy of mixing.
Abstract: The integral enthalpies of mixing in the six binary systems formed by MgCl2, CaCl2, SrCl2, and BaCl2 have been determined calorimetrically. The results are discussed in terms of the theories of Reiss, Katz, and Kleppa and of Davis and Rice, each suitably modified to take into account the higher charge on the cation. The molar enthalpies of mixing for the systems CaCl2-SrCl2, CaCl2-BaCl2, and SrCl2-BaCl2 can be represented by the following approximate expression which is simply related to the corresponding expression for the binary alkali halides, previously derived by Hersh and Kleppa:
ÎHmix = X1 X2 [ (Uo++) - (Z*2)340( δ12*2)] kcak/mole
Here X1 and X2 are the mole fractions of the two components; δ12=(d1âd2) / d1d2, where d1 and d2 are the sums of the ionic radii of anion and cation in the two salts, while Z=Z1Z2, the product of the charges of the anion and cation in the component salts (here Z=2). The term Uο++ represents an estimate of the contribution to the enthalpy of mixing arising from the London dispersion interaction between next-nearest-neighbor cations. The quoted expression does not hold for the three binary systems involving MgCl2, which are all much less exothermic and which exhibit considerable energetic asymmetry. In all cases the enthalpy of solution of MCl2 in MgCl2 is more endothermic than the opposite process. The results for these three systems are interpreted to support the view, originally advanced by Frland, that pure MgCl2 has a certain tendency to form covalently bonded Mg-Cl-Mg bridges. The breaking of these bridges gives rise to a significant endothermic contribution to the enthalpy of mixing, over and above the contributions arising from Coulombic and dispersion forces
Abstract: The Raman spectra of the amorphous phases (glassy, supercooled and molten) silica have been measured from LN2 temperature to above the melting point. A new carbon dioxide laser-heating system has been developed for measuring in situ polarized and depolarized spectra at high temperature with relatively low black body radiation background. The reduced anisotropic spectra show that the relative intensities of three bands in the Si-O symmetric stretching frequency region change with temperature. A comparison with the spectral features of other tetrahedral glasses and melts has revealed that the silica network consists of tetrahedra bound to each other by apex- and edge-bridged oxygen atoms. The substructure of the glass/melt is formed by mixing the well established three- and four-membered rings with a variety of tetrahedra participating in âopenâ, âclusterâ and âchainâ networks which are bound to each other by bridging oxygens. Different rates of inter-structural changes with temperature are observed below and above glass transition temperature. Finally, the low-frequency spectra reveal that the Boson peak persists, well resolved in the supercooled liquid and to the normal state melt. The Boson peak region is discussed in the framework of recent relevant models and theoretical correlations.
