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 ...
Phonon Interference in BATIO3 - High-Pressure Raman-Study
Physical Review B, 1995
Raman experiments have been carried out on single crystals of BaTi03 as a function of pressure up to 3.5 GPa across the ferroelectric (tetragonal) to paraelectric (cubic) phase transition. The unusual features in the Raman spectra associated with the interference effects due to coupling of the three Aq(TO) phonons are studied quantitatively to obtain the pressure dependence of the line shape parameters and the coupling constants. The frequencies of the middle and highest-frequency modes as well as the linewidth of the middle mode show interesting pressure dependence. INTBODU CTION BaTi03 is one of the most important ferroelectric materials of the perovskite family. At ambient pressure, there are three structural phase transitions with increasing temperature at about 193 K (rhombohedral: orthorhombic), 280 K (orthorhombic, ' tetragonal), and
Pressure-Induced Phase Transitions in ScF 3 Crystal--Raman Spectra and Lattice Dynamics
2003
New pressure-induced phases are found in normally cubic ScF 3 crystal using polarizing microscopy and micro-Raman spectroscopy. Their supposed space groups are R3c, Z = 2 and Pnma, Z = 4. Using ab initio model cubic phase was shown to be stable at ambient pressure down to T = 0 K, while hydrostatic pressure brings one of the phonon branches down to negative squared frequencies. R 5 soft mode condensation results in the rhombohedric distortion of the cubic lattice with cell volume doubling. Calculated squared frequencies of the high pressure phase are positive, their number and values agree with experimental results.
A first principles calculation of the lattice dynamical properties of rutile SnO 2 has been performed using density functional perturbation theory at ambient and high-pressure conditions to understand the pressure-induced phase transition. The calculated zone centre phonon modes at ambient and high pressures have been compared with Raman scattering and infrared measurements. Full phonon dispersion curves and phonon densities of states and Raman intensities at high pressures are calculated and given for the first time in literature. The ferroelastic transition from the rutile to the CaCl 2-type structure was confirmed. It is clearly illustrated that the first transition is associated with macroscopic shear instability which arises from the strong coupling between elastic constants and softening of Raman active B 1g mode. The observed pressure of phase transition in experimental measurements was reproduced more accurately than in previous calculations, and the difference between observed and calculated transition pressure is only of the order of 2%. The mode Grüneisen parameter is quantitatively as well as qualitatively different from the earlier reported values.
Pressure-induced changes in the optical properties of quasi-one-dimensional β-Na0.33V2O5
Physical Review B, 2007
The pressure-induced changes in the optical properties of β-Na0.33V2O5 single crystals at room temperature were studied by polarization-dependent Raman and far-infrared reflectivity measurements under high pressure. From the changes in the Raman-and infrared-active phonon modes in the pressure range 9 -12 GPa a transfer of charge between the different V sites can be inferred. The importance of electron-phonon coupling in the low-pressure regime is discussed. *
Phonon triggered rhombohedral lattice distortion in vanadium at high pressure
Scientific Reports, 2016
In spite of the simple body-centered-cubic crystal structure, the elements of group V, vanadium, niobium and tantalum, show strong interactions between the electronic properties and lattice dynamics. Further, these interactions can be tuned by external parameters, such as pressure and temperature. We used inelastic x-ray scattering to probe the phonon dispersion of single-crystalline vanadium as a function of pressure to 45 GPa. Our measurements show an anomalous high-pressure behavior of the transverse acoustic mode along the (100) direction and a softening of the elastic modulus C 44 that triggers a rhombohedral lattice distortion occurring between 34 and 39 GPa. Our results provide the missing experimental confirmation of the theoretically predicted shear instability arising from the progressive intra-band nesting of the Fermi surface with increasing pressure, a scenario common to all transition metals of group V. Although body-centered-cubic (bcc) metals have one of the simplest crystal structures in the periodic table, they display a rich variety of physical properties and thus provide an important benchmark for the validation of modern first-principle theory 1. In particular, the lattice dynamics of bcc transition metals have attracted great scientific attention. The Kohn anomaly in the phonon dispersion of bcc transition metals, and its dependence upon pressure and temperature, has been a challenge for first principle calculations to capture 2,3. The strong differences displayed by the phonon dispersion of the various elements of group V (vanadium, niobium and tantalum) suggest that there is a profound dependence of the phonon energies on the electronic structure and the topology of the Fermi surface 4,5. The high superconducting temperature (T c = 9.25 K for Nb and T c = 5.3 K for V) and its notable increase with pressure have also been suggested to be due to electron-phonon coupling and Fermi-surface properties 6-8. The stability at high pressure of the bcc structure is speculated to critically hinge on the topology of the Fermi surface as well, and an intra-band nesting is theoretically predicted to give rise to shear phonon instabilities 9. Focusing on vanadium, calculations of shear instabilities arising from phonon softening 9 have prompted the reinvestigation of the structural stability of V under high pressure. X-ray powder diffraction showed a transition from the bcc to a rhombohedral phase at 69 GPa 10 and subsequent calculations have confirmed the nature of the rhombohedral distortion-even though different transition pressures were proposed 5,11-13. Interestingly, under hydrostatic conditions the transition is hindered, and non-hydrostaticity helps in overcoming the energy barrier associated with the structural phase change 14. Irrespective of the exact pressure at which the transition occurs, the bulk of theoretical work points towards a common mechanism: the progressive intra-band nesting at the Fermi surface that eventually leads to an electronic topological transition (ETT) with a concomitant transverse acoustic phonon mode softening. Specifically, at a critical pressure, parts of the 3rd electronic, partially occupied, conduction band of d symmetry move into the close vicinity of the Fermi level. The nesting vector, already responsible for the Kohn anomaly in the transverse acoustic phonon mode along the (ξ, 0, 0) direction at ξ = 0.25 at ambient pressure 8 , reduces to zero and the ETT takes place, with instability in the shear elastic constant C 44 9. This anomalous softening of the elastic response causes an energy gain that counterbalances the standard elastic strain energy
Pressure-tuning FT-Raman spectroscopic study of the T2g phonon mode of a diamond-anvil cell
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 1997
The stress behaviour of a type-IIA diamond in a commercial diamond-anvil cell has been examined by measuring the position of the TZg phonon mode of the top diamond in the cell (originally located at-1332 cm-') during a pressure-tuning FT-Raman microspectroscopic study at various pressures throughout the 0.001-62.2 kbar range. In general, the components of the scattered Raman signal from different depths appear as discrete band envelopes rather than a continuous gradient throughout the depth of the diamond. The changes taking place in the band structure with the variation in depth indicate the occurrence not of phase changes but of discontinuities in the pressure gradient throughout the diamond. For measurements made at the bottom edge of the diamond (i.e. at the sample-diamond interface), there is a linear relationship between the position (v, wavenumbers) of the T,, phonon mode and the pressure (P, kbar) such that dv/dP = 0.16 cm-' kbar-'.
Journal of Raman Spectroscopy, 2003
Raman spectroscopy is a powerful tool for the study of solids under extreme conditions of pressure and temperature. This technique can be used to determine phase diagrams and study phase transition mechanisms. Raman spectroscopy can be used to characterize disorder present in crystalline solids and is sensitive to local structural configurations. The combined use of diamond anvil cells and closed-cycle helium cryostats enables Raman scattering experiments to be performed at pressures exceeding 50 GPa in the 10-300 K temperature range. The use of this technique to study the perovskite-type piezoelectric material PbZr 0.52 Ti 0.48 O 3 enables the monoclinic and cubic phases present in this system to be characterized and their pressure-temperature domains of stability to be defined. Raman scattering results indicate the presence of polar domains in the cubic, high-pressure phase. The ferroelectric monoclinic phases exhibit extended stability at high pressure and low temperature.
We report the experimental studies of the vibrational spectra of SrTiO 3 films with the thickness of 1 µm grown by pulsed laser deposition. Fourier-transform infrared ellipsometry between 30 and 700 cm-1 and electric field-induced Raman scattering techniques have been utilized for investigation of the phonon behavior. These results can be used for comparison with the low-frequency measurements of the static dielectric constant. The soft mode in the films reveals hardening compared to that in bulk crystals. This observation is in agreement with the Lyddane-Sachs-Teller formalism.
Journal of Raman Spectroscopy, 2012
Raman spectra of Rb 2 KTiOF 5 crystal were obtained and analyzed in the temperature range from 77 to 297 K and under hydrostatic pressure up to 4.2 GPa (at T = 295 K). The experimental results were compared with quantum-chemical simulation of TiOF 5 pseudo-octahedron. To interpret effects of lattice ordering, phonon spectra of several ordered phases of Rb 2 KTiOF 5 were calculated within ab initio generalized Gordon-Kim model, and ordering of TiOF 5 molecular groups were simulated within Monte Carlo approach. The spectra exhibited orientation disordering in the cubic phase under ambient conditions. Cooling below the phase transition temperature (215 K) leads to partial ordering of the structure. The isotropic perovskite-like phase was found to undergo first-order transition into a low-symmetry anisotropic phase at about 1 GPa. Further compression up to 4.1 GPa did not show any effects associated with phase transitions.
Structural stability of Sc 3 CrO 6 : A Raman spectroscopic study
Journal of Raman Spectroscopy, 2020
Structural stability of the mixed rare earth-transition metal oxide Sc 3 CrO 6 (space group R3c) is investigated at high pressures using Raman spectroscopy up to 23.8 GPa, at ambient temperature. Results indicate that the compound transforms reversibly to a lower symmetry phase above 18 GPa. Lattice dynamical calculations carried out using a shell model were used to obtain the bulk modulus and to estimate mode Grüneisen parameters from Raman spectroscopic data. From the nature of changes in the vibrational spectra and from the trends in iso-structural compounds, we speculate the high pressure phase to be a monoclinic phase. On the other hand, temperature dependent Raman scattering studies in the temperature range 77-1,273 K, indicate disappearance of a few vibrational modes indicating increase in symmetry. From the pressure and temperature dependence of the Raman modes, using calculated bulk modulus and thermal expansion coefficient, anharmonicity of the modes is estimated. It is found that anharmonicity due to phonon-phonon decay is more dominant and the contribution of thermal expansion is small for all of the Raman modes.