High-pressure Raman spectra

FT Raman (near-IR excitation) and UV-Raman spectra were used to study tetragonal-monoclinic transitions in (Zr02)o.98(M203)o.o2, where M = Sc or Y. It was found that the temperature of the transition depends on the calcination temperature of the samples.4 High-pressure Raman spectra of Sc2(Mo04)3 gave evidence for two phase transitions, leading to an amorphous state.5... 

The crystallinity of MW04 (M=Ba, Pb) thin films was studied by IR spectroscopy.223 High-pressure Raman spectra of A12(W04)3 showed phase transitions at 0.28 0.07 and 2.8 0.1 GPa.224 The IR spectrum of the double perovskite Sr2FeW06 includes characteristic bands at 143, 227, 377 and 625 cm-1.225... 

Walrafen GE, Hokmabadi MS, Yang WH, Piermarini GJ (1988) High-temperature high-pressure Raman spectra from liquid water. J Phys Chem 92 4540-4542 Walrrfen GE, Chu YC (1995) Linearity between structural correlation length and correlated-proton Raman intensity from amorphous ice and supercooled water up to dense supercritical steam. J Phys Chem 99 11225-11229... 

The high-pressure Raman spectra of MLn(W04)2, where M = Na or K Ln = Sm, Tb or Ho, gave evidence of phase transitions near 10 GPa. " Raman spectroscopy was also used to monitor high-temperature phase transitions of SmF3. ... 

Figure 12.5 shows the high-pressure Raman spectra of Ge QDs up to 67 kbar using the laser excitation at 2.41 eV without polarization. At ambient pressure, four peaks are identified Ge-Ge or Si-2TA (304 cm ), Si-Ge (419 cm ). 

Figure 12.6. Representative high-pressure Raman spectra of Ge QDs with different laser excitation energies, [3].

DFT calculations gave vibrational wavenumbers for (HCNBH)n and (BH2CN)n, where n = 1 6.38 The high-pressure Raman spectrum of BH3.NH3... 

Oxygen. - IR spectroscopy was used to characterise 02 molecules trapped in vacancies in silicon crystals.607 The high-pressure Raman spectrum of 02 (to 134 GPa) shows significant Raman intensity in the metallic phase, showing that this still retains molecular character.608 High-resolution IR spectra were reported for a number of isotopomers of 03 for a variety of fundamental and overtone/combination bands.609 611... 

The high-pressure Raman spectrum of Li2S reveals a phase transition from the antifluorite to an orthorhombic structure at about 12 GPa. The dimeric species [(TMEDA)LiCl]2, where TMEDA = tetramethylethylenediamine, gives IR bands due to vLi2Cl2 at 334 and 397 cm" (the latter mixed with vLiN). ... 

Other Sulfur and Selenium Compounds. - The high-pressure Raman spectrum of D2S gave evidence for dissociation to sulfur at pressures above 27 GPa at room temperature. A normal coordinate analysis for crystalline H2S and D2S gave good agreement with experimental data. ... 

The IR spectrum of Ba3[BN2]2 shows low site symmetry for the BN23 groups.68 Vibrational data for Eu3[BN2]2, however, were interpreted in terms of discrete BN23- units of D jh symmetry.69 IR data were reported for a 1,3,2-oxazaborolidine dimer derived from (V)-a,a-diphenylprolinol.70 The IR and Raman spectra of the new adduct P8012.2BH3 included vPB at 565 cm-1 (IR), 574 cm-1 (Raman), as well as characteristic vBH bands.71 High-pressure Raman spectroscopy was used to follow pressure-induced phase transitions for B12As2.72... 

IR and Raman spectra were used to characterise GaN nanocrystals grown by chloride-hydride vapour-phase epitaxy on oxidised silicon.138 High-pressure Raman spectroscopy was used to follow the wurtzite to rock salt phase transition for epitaxial GaN.139 The Raman spectrum of prism-shaped GaN nanorods included characteristic bands at 255 and 419 cm-1.140 Raman spectroscopy was used to characterise GaNi xPx alloys.141 143... 

High-pressure Raman studies have been made to follow phase transitions of MgSi03.460 462 Molecular dynamics calculations have been performed on the vibrational spectrum of CaSi03 over the melt to glass transition.463... 

Far-IR data were reported and discussed for two- and one-dimensional Cao polymers. The Raman spectrum of two-dimensional polymerised C60 shows a phase transition at 19.0-21.0 GPa - possibly to a three-dimensional system of Cao cages. Calculated Raman spectra were reported for orthorhombic, tetragonal and rhombohedral phases of pressure-polymerised C6o. ° High-pressure Raman spectroscopy on two-dimensional tetragonal polymeric Cm showed a... 

High-pressure Raman spectroscopy on nanocrystalline Ce02 was used to observe a phase transition near 26.5 GPa. The Raman spectrum of nanometer... 

Asell J F and Nicol M 1968 Raman spectrum of a-quartz at high pressures J. Chem. Phys. 49 5395... 

Fig. 29 Raman spectrum of p-S at high pressure and room temperature [109]. The wavenumbers indicated are given for the actual pressure. No signals of other allotropes have been detected. The line at 48 cm (ca. 25 cm atp 0 GPa) may arise from lattice vibrations, while the other lines resemble the typical pattern of internal vibrations of sulfur molecules...

Since the vibrational spectra of sulfur allotropes are characteristic for their molecular and crystalline structure, vibrational spectroscopy has become a valuable tool in structural studies besides X-ray diffraction techniques. In particular, Raman spectroscopy on sulfur samples at high pressures is much easier to perform than IR spectroscopical studies due to technical demands (e.g., throughput of the IR beam, spectral range in the far-infrared). On the other hand, application of laser radiation for exciting the Raman spectrum may cause photo-induced structural changes. High-pressure phase transitions and structures of elemental sulfur at high pressures were already discussed in [1]. 

At least five high-pressure allotropes of sulfur have been observed by Raman spectroscopy up to about 40 GPa the spectra of which differ significantly from those of a-Sg at high pressures photo-induced amorphous sulfur (a-S) [57, 58, 109, 119, 184-186], photo-induced sulfur (p-S) [57, 58, 109, 119, 184, 186-191], rhombohedral Se [58, 109, 137, 184, 186, 188, 191], high-pressure low-temperature sulfur (hplt-S) [137, 184, 192], and polymeric sulfur (S ) [58, 109, 119, 193]. The Raman spectra of two of these d-lotropes, a-S and S, were discussed in the preceding section. The Raman spectra of p-S and hplt-S have only been reported for samples at high-pressure conditions. The structure of both allotropes are imknown. The Raman spectrum of Se at STP conditions is discussed below. 

Fig. 31 Evolution of the Raman spectra of a high-pressure and photo-induced sample of Se while decreasing the pressure at ca. 300 K [109]. The spectrum at 3.9 GPa shows the onset of the transformation S6 p-S. The asterisks indicate the Raman signals typical for p-S whereas the peaks of two stretching vibrations of p-S coincide with those of Se at about 458 cm and 471 cm (not indicated by asterisks). The Raman spectrum of the sample recovered at ambient pressure (0 GPa) is evidently a superposition of the spectra of a-Sg and polymeric sulfur, Sj, arrows indicate plasma lines of the Ar ion laser at 515 nm, which have been used for calibration). For Raman spectra under increasing pressure, see Fig. 23 in [1] and references cited therein...

Experiments at high pressure have shown that the P-T phase diagram of butadiene is comparatively simple. The crystal phase I is separated from the liquid phase by an orientationally disordered phase II stable in a narrow range of pressure and temperature. The strucmre of phase I is not known, but the analyses of the infrared and Raman spectra have suggested a monoclinic structure with two molecules per unit cell as the most likely [428]. At room temperature, butadiene is stable in the liquid phase at pressures up to 0.7 GPa. At this pressure a reaction starts as revealed by the growth of new infrared bands (see the upper panel of Fig. 25). After several days a product is recovered, and the infrared spectrum identifies it as 4-vinylcyclohexene. No traces of the other dimers can be detected, and only traces of a polymer are present. If we increase the pressure to 1 GPa, the dimerization rate increases but the amount of polymer... 

The Raman spectrum of CaMo04 and CaW04 (198) has been measured up to about 40 Kbar with a dvjdp of between 0.1—1 cm i Kbar i. A new high pressure phase was discovered in the course of this study. Attempts to predict the sign of dvjdp for the internal vibration by the Davydov-sphtting model fell through (196). 

The comparison of our experimental data with those of Ref. (Bini et al. 1998 Bensasson et al. 1997) shows that the Raman spectrum of the high-pressure hydrogenated C60H36 is richer more than five times than that of the transfer hydrogenated C60H36. The majority of the experimentally observed Raman peaks (86 peaks from a total number of 126) are very close, with an accuracy of 5 cm-1, to the calculated frequencies and cross-sections of the Raman active modes (their total number is 400) (Bini et al. 1998). The peaks, which are close to the calculated frequencies, are assigned to all principal isomers, but the majority of them belong to the isomers with the symmetry S6, T and D3d. 

Figure 6. Raman spectrum of a sillimanite elongated and curved inclusion indicating a high Pressure-Temperature metamorphism of the crystal...

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