Raman study of β-Sr0.33V2O5 micro-crystals under high pressure (original) (raw)

Raman study of beta-Sr0.33V2O5 micro-crystals under high pressure

Physica Status Solidi B-basic Solid State Physics, 2007

The phonon dynamics of the strontium vanadium oxide bronze (β-Sr0.33V2O5) is studied using Raman spectroscopy at different temperature under high pressure up to 5.7 GPa. Interesting features of the spectra, such as the narrowing of some modes that harden under pressure (250–300 cm–1) or the softening of a low-frequency mode, are presented and discussed. Our low temperature measurements confirm that under high hydrostatic pressure the charge ordered phase is suppressed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Raman Studies of Vanadates at Low Temperatures and High Pressures

Journal of Superconductivity and Novel Magnetism, 2009

The spin and orbital ordering have been examined for high-quality SmVO 3 polycrystalline compound using Raman spectroscopy. Measurements were obtained on individual microcrystallites in the approximate y(zz)y and y(xx)y scattering configurations at low temperatures (down to 20 K) and high pressures (up to 2.75 GPa). At room temperature and ambient pressure only the A g phonons have been observed in both polarizations examined. The decrease of temperature leads to the appearance of extra peaks in the Raman spectra related to the magnetic and structural transitions that occur in the system. We present evidence of a coexistence of the monoclinic and orthorhombic phases accompanied with the coexistence of the G-and C-type OO phases for temperatures below 100 K. However, no sign of any structural transition has been observed in the high pressure Raman spectra (1.87 < P < 2.75 GPa) at low temperatures T ≥ 80 K, indicating that SmVO 3 remains orthorhombic, at least down to 80 K.

Raman scattering in osmium under pressure

Physical Review B, 2005

The effect of pressure and temperature on the Raman-active phonon mode of osmium metal has been investigated for pressures up to 20 GPa and temperatures in the range 10-300 K. Under hydrostatic conditions (He pressure medium) the phonon frequency increases at a rate of 0.73(5) cm −1 /GPa (T = 300 K). A large temperature-induced and wavelength-dependent frequency shift of the phonon frequency is observed, of which only a small fraction can be associated with the thermal volume change. The main contribution to the temperature dependence of the phonon frequency is rather attributed to non-adiabatic effects in the electron-phonon interaction, which explains also the observation of an increasing phonon line width upon cooling. The phonon line width and the pressure-induced frequency shift were found to be unusually sensitive to shear stress.

Structural and vibrational study of cubic Sb_ {2} O_ {3} under high pressure

2012

We report an experimental and theoretical study of antimony oxide (Sb 2 O 3) in its cubic phase (senarmontite) under high pressure. X-ray diffraction and Raman scattering measurements up to 18 and 25 GPa, respectively, have been complemented with ab initio total-energy and lattice dynamics calculations. X-ray diffraction measurements do not provide evidence of a space-group symmetry change in senarmontite up to 18 GPa. However, Raman scattering measurements evidence changes in the pressure coefficients of the Raman mode frequencies at 3.5 and 10 GPa, respectively. The behaviour of the Raman modes with increasing pressure up to 25 GPa is fully reproduced by the lattice-dynamics calculations in cubic Sb 2 O 3. Therefore, the combined analysis of both experiments and lattice-dynamics calculations suggest the occurrence of two isostructural phase transformations at 3.5 and 10 GPa, respectively. Total-energy calculations show that the isostructural phase transformations occur through local atomic displacements in which senarmontite losses its molecular character to become a three-dimensional solid. In addition, our calculations provide evidence that cubic senarmontite cannot undergo a phase transition to orthorhombic valentinite at high pressure, and that a phase transition to a β-Bi 2 O 3 type structure is possible above 25 GPa.

Phase progression via phonon modes in lanthanide dioxides under pressure

The present paper reports the phase progression in nano-crystalline oxides PrO 2 and CeO 2 up to pressures of 49 GPa and 35 GPa, respectively, investigated via in situ Raman spectroscopy at room temperature. The samples were characterized at ambient conditions using X-ray diffraction (XRD), AFM, and Raman spectroscopy and were found to be cubic with fluorite structure. With an increase in applied pressure the cubic bands were seen to steadily shift to higher wavenumbers for both the samples. However, we observed the appearance of a number of new peaks around a pressure of about 34.7 GPa in CeO 2 and 33 GPa in PrO 2 which were characteristic of an orthorhombic ␣-PbCl 2 type structure. The mode Gruneisen parameters for both the phases were obtained from the pressure dependence of frequency shifts. On decompression, the high pressure phase existed down to a total release of pressure.

High pressure lattice dynamics, dielectric and thermodynamic properties of SrO

Physica B-condensed Matter, 2011

Using density functional theory and density functional perturbation theory we have studied the effects of hydrostatic pressure on lattice dynamics, dielectric and thermodynamic properties of the rocksalt (NaCl) and CsCl phases of SrO. The stability of the NiAs type structure, experimentally confirmed to be stable in BaO, is also investigated. Studying the lattice dynamics of the NaCl and CsCl phases at various pressures, in the range of the phase stability, we have found the lattice dynamical instabilities which govern the phase transitions between NaCl and CsCl phases with increasing and decreasing pressure. By monitoring the behaviour of the found soft modes, we have calculated the transition pressures upon compression and decompression of SrO crystal. Lattice dynamics calculations reveal that the rocksalt and CsCl structures are unstable with respect to the soft transversal acoustic modes at single points of the Brillouin zone, which points to the fact that the transitions are of displacive type. Responses to electric fields and thermodynamic properties at high pressures are also given and discussed. All our results are in a good agreement with experimental data where applicable.

High-pressure study of ScVO_{4} by Raman scattering and ab initio calculations

Physical Review B, 2011

We report results of experimental and theoretical lattice-dynamics studies on scandium orthovanadate up to 35 GPa. Raman-active modes of the low-pressure zircon phase are measured up to 8.2 GPa, where the onset of an irreversible zircon-to-scheelite phase transition is detected. Raman-active modes in the scheelite structure are observed up to 16.5 GPa. Beyond 18.2 GPa we detected a gradual splitting of the E g modes of the scheelite phase, indicating the onset of a second phase transition. Raman symmetries, frequencies, and pressure coefficients in the three phases of ScVO 4 are discussed in the light of ab initio lattice-dynamics calculations that support the experimental results. The results on all the three phases of ScVO 4 are compared with those previously reported for related orthovanadates.

Lattice vibrations of high-pressure SiO2 phases: Raman spectrum of synthetic stishovite

1986

Raman spectra of synthetic stishovite, the high-pressure phase of SiO 2 with the rutile structure, have been measured with a micro-optical spectrometer system. In contrast to previously reported Raman results obtained on natural samples, the spectra measured here have a pattern that is characteristic of rutile-structured oxides. Bands at 231,589, 753, and 967 cmare resolved, and are assigned as the B~, Eg, A ,g, and B2~ fundamentals, respectively, of the first-order Raman spectrum of the ideal, ordered structure.

Pressure-temperature phase diagram of SrTiO_ {3} up to 53 GPa

Physical Review B, 2010

We investigate the cubic to tetragonal phase transition in the pressure-temperature phase diagram of strontium titanate SrTiO 3 (STO) by means of Raman spectroscopy and x-ray diffraction on single-crystal samples. X-ray diffraction experiments are performed at room ...