The pressure tunning Raman spectral studies of the bilirubinIXα and neutral calcium bilirubinate at high external pressure (original) (raw)
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High pressure raman study of Bi-2212
High Pressure Research, 2003
The hydrostatic pressure dependence of the Raman spectra of Bi 2 Sr 2 CaCu 2 O 8 single crystals has been investigated. The energy of the A g and B 1g modes was found to increase with pressure in agreement with previously reported measurements, except the strong mode at 465cmAˋ1,whichsoftenswithpressure,whileanotherpeakat465 cm À1 , which softens with pressure, while another peak at 465cmAˋ1,whichsoftenswithpressure,whileanotherpeakat458 cm À1 appears more pronounced at low temperatures and high pressures. The energy of both modes does not seem to change with increasing pressure, up to 5GPa,althoughtheaverageenergyofthewidebandhasbeenfoundtosoften,whichisindisagreementwithpreviouslypublishedresults.Basedonthemodificationsobservedinsomephononsat5 GPa, although the average energy of the wide band has been found to soften, which is in disagreement with previously published results. Based on the modifications observed in some phonons at 5GPa,althoughtheaverageenergyofthewidebandhasbeenfoundtosoften,whichisindisagreementwithpreviouslypublishedresults.Basedonthemodificationsobservedinsomephononsat1.8 GPa, which correlate with the reduction of T c and the deformations of the CuO 5 pyramids, we attribute the mode at $465 cm À1 to the vibrations of the apex oxygen atoms. All modes due to the oxygen atoms were found to be strongly anharmonic.
Journal of Physical Chemistry C, 2010
Calcium borohydride (Ca(BH 4 ) 2 ) has attracted significant interest in recent years due to its strong potential for hydrogen storage applications. Here, we report the pressure-induced structural transformations of Ca(BH 4 ) 2 probed by combined Raman spectroscopy and infrared (IR) spectroscopy up to 10.4 GPa at room temperature. Starting with the R phase in an orthorhombic structure, Ca(BH 4 ) 2 was found to undergo several transformations upon compression, as evidenced by the sequential changes of characteristic Raman and IR modes as well as by examining the pressure dependences of these modes. In situ Raman and IR measurements collectively provided consistent information about the structural evolutions of Ca(BH 4 ) 2 under compression. Decompression measurements on Ca(BH 4 ) 2 suggest that the pressure-induced transformations are reversible in the entire pressure region. The combined Raman and IR data allowed for an in-depth analysis of possible high-pressure structures of Ca(
EFFECT OF PRESSURE ON RAMAN-SPECTRA OF SOLID HCl AND HBr
Le Journal de Physique Colloques, 1984
-Des résultats de diffusion Raman sur HC1 et HBr, a des températures de 100 à 250 K et des pressions jusqu'à 40 GPa sont présentés. Une nouvelle procédure de chargement avec ces produits réactifs est décrite. L'argon et l'azote sont utilisés comme milieux transmetteurs de pression. Dans HBr, une nouvelle phase a été détectée-probablement avec des liaisons hydrogène symétriques-à 100 K et è des pressions supérieures à 32 GPa.
High-pressure behavior of bikitaite: An integrated theoretical and experimental approach
2002
Pressure-induced structural modifications in the zeolite bikitaite are studied by means of in situ synchrotron X-ray powder diffraction and ab initio molecular dynamics. The experimental cell parameters were refined up to 9 GPa, at which pressure we found reductions of 4.5, 4.5, 6.3, and 15% in a, b, c, and V, respectively. Minor variations were observed for the cell angles. Complete X-ray amorphization is not achieved in the investigated P range, moreover the P-induced effects on the bikitaite structure are completely reversible. Because it was possible to extract only the cell parameters from the powder patterns, the atomic coordinates at 5.7 and 9.0 GPa were obtained by means of Car-Parrinello simulations using the unit-cell parameters experimentally determined at these pressures. Analysis of the computational results for increasing pressures showed that the volume contraction is essentially due to rotations of the tetrahedra; the 8-ring channels become more circular; the pyroxene chain becomes more corrugated in the b-c plane; and the mean Li-O bond distances and coordination polyhedral volumes decrease with increasing pressure without significant distortion of the internal angles. The peculiar aspect of the bikitaite structure, i.e., the presence in the channels of a “floating” one-dimensional water chain, is only partially maintained at high pressure; the compression brings framework O atoms close enough to water hydrogen atoms to allow the formation of host-guest hydrogen bonds, without, however, destroying the one-dimensional chain.
High-Pressure Studies of Bi 2 S 3
The Journal of Physical Chemistry A, 2014
The high-pressure structural and vibrational properties of Bi 2 S 3 have been probed up to 65 GPa with a combination of experimental and theoretical methods. The ambient-pressure Pnma structure is found to persist up to 50 GPa; further compression leads to structural disorder. Closer inspection of our structural and Raman spectroscopic results reveals notable compressibility changes in specific structural parameters of the Pnma phase beyond 4−6 GPa. By taking the available literature into account, we speculate that a second-order isostructural transition is realized near that pressure, originating probably from a topological modification of the Bi 2 S 3 electronic structure near that pressure. Finally, the Bi 3+ loneelectron pair (LEP) stereochemical activity decreases against pressure increase; an utter vanishing, however, is not expected until 1 Mbar. This persistence of the Bi 3+ LEP activity in Bi 2 S 3 can explain the absence of any structural transitions toward higher crystalline symmetries in the investigated pressure range.
Raman Studies of Molecular Crystals at High Pressures. IV. Acetonitrile,CH3CN andCD3CN
Journal of Raman Spectroscopy, 1996
The vibrations of solid tribromofluoromethane were studied by Raman scattering at room temperature and up to pressures of about 9 GPa. Changes in the low-wavenumber region of the Raman spectra reveal that freezing occurs near 1.0 GPa and that a solid-state phase transition occurs near 1.8 GPa. All of the internal modes are found to display splitting at elevated pressures, although only two modes (the CBr, asymmetric stretch v4 and the CF stretch vl) display splitting at the lowest pressures of the solid phase. The wavenumbers of the lattice and internal modes increase with applied pressure, except for the CF stretch mode vi, which decreases uniformly as the pressure increases.
Acta Crystallographica Section B Structural Science, 2010
The crystal structure of the high-pressure phase of bismuth gallium oxide, Bi2Ga4O9, was determined up to 30.5 (5) GPa fromin situsingle-crystal in-house and synchrotron X-ray diffraction. Structures were refined at ambient conditions and at pressures of 3.3 (2), 6.2 (3), 8.9 (1) and 14.9 (3) GPa for the low-pressure phase, and at 21.4 (5) and 30.5 (5) GPa for the high-pressure phase. The mode-Grüneisen parameters for the Raman modes of the low-pressure structure and the changes of the modes induced by the phase transition were obtained from Raman spectroscopic measurements. Complementary quantum-mechanical calculations based on density-functional theory were performed between 0 and 50 GPa. The phase transition is driven by a large spontaneous displacement of one O atom from a fully constrained position. The density-functional theory (DFT) model confirmed the persistence of the stereochemical activity of the lone electron pair up to at least 50 GPa in accordance with the crystal str...
Journal of Raman Spectroscopy, 2010
The series of phase transitions on increasing pressure and on reverse decompression was followed in crystals of monoclinic and orthorhombic polymorphs of L-cysteine by using Raman spectroscopy, with the samples placed in a diamond anvil cell together to ensure identical pressures on the two samples. The effects of hydrostatic pressure on the two polymorphs are shown to be radically different. Depending on the starting polymorph, different phases are formed under identical compression/decompression conditions. The effect of pressure on the monoclinic polymorph was studied for the first time. Phase transitions in monoclinic L-cysteine (at ∼2.9 and ∼3.9 GPa) are completely reversible without a noticeable hysteresis.
Acta Crystallographica Section B Structural Science, 2012
Information on the effect of pressure on hydrogen bonds, which could be derived from single-crystal X-ray diffraction at a laboratory source and polarized Raman spectroscopy, has been compared. l-Serine and dl-serine were selected for this case study. The role of hydrogen bonds in pressure-induced phase transitions in the first system and in the structural stability of the second one are discussed. Non-monotonic distortion of selected hydrogen bonds in the pressure range below $ 1-2 GPa, a change in the compression mechanism at $ 2-3 GPa, and the evidence of formation of bifurcated N-HÁ Á ÁO hydrogen bonds in dl-serine at $ 3-4 GPa are considered. research papers Acta Cryst. (2012). B68, 275-286 Zakharov et al. Effect of pressure on serine 285
Pressure effects on the vibrational properties ofα-Bi2O3: an experimental and theoretical study
Journal of Physics: Condensed Matter, 2014
We report an experimental and theoretical high-pressure study of the vibrational properties of synthetic monoclinic bismuth oxide (α-Bi 2 O 3), also known as mineral bismite. The comparison of Raman scattering measurements and theoretical lattice-dynamics ab initio calculations is key to understanding the complex vibrational properties of bismite. On one hand, calculations help in the symmetry assignment of phonons and to discover the phonon interactions taking place in this low-symmetry compound, which shows considerable phonon anticrossings; and, on the other hand, measurements help to validate the accuracy of firstprinciples calculations relating to this compound. We have also studied the pressure-induced amorphization (PIA) of synthetic bismite occurring around 20 GPa and showed that it is reversible below 25 GPa. Furthermore, a partial temperature-induced recrystallization (TIR) of the amorphous sample can be observed above 20 GPa upon heating to 200°C, thus evidencing that PIA at room temperature occurs because of the inability of the α phase to undergo a phase transition to a high-pressure phase. Raman scattering measurements of the TIR sample at room temperature during pressure release have been performed. The interpretation of these results in the light of ab initio calculations of the candidate phases at high pressures has allowed us to tentatively attribute the TIR phase to the recently found high-pressure hexagonal HPC phase and to discuss its lattice dynamics.