A raman study of hydrostatic pressure induced phase transitions in Rb2KInF6 crystals

The Raman spectra of the elpasolite (Rb₂KInF₆) crystal have been studied in the pressure range from 0 to 5.3 GPa at a temperature of 295 K. A phase transition at a pressure of approximately 0.9 GPa has been found. An analysis of the variations in the spectral parameters has led to the conclusion that the phase transition to a distorted phase is accompanied by the doubling of the volume of the primitive cell of the initial cubic phase. Numerical calculations of the lattice dynamics in the Rb₂KInF₆ crystal have been performed. The numerical simulation has established that the phase transition at a pressure of 0.9 GPa is associated with condensation of the F _lg mode. A probable high-pressure phase is the phase with space group C2/m.     

Lattice dynamics and hydrostatic-pressure-induced phase transitions in ScF3

New phase transitions induced by hydrostatic pressure in a cubic (under standard conditions) ScF₃ crystal are discovered by the methods of polarization microscopy and Raman scattering. The space groups $R\bar 3c$ for Z=2 and Pnma for Z=4 are proposed for the high-pressure phases. A nonempirical computation of the lattice dynamics of the crystal is carried out. It is shown that, under normal pressure, the cubic phase is stable down to T=0 K, while the application of a hydrostatic pressure gives rise to a phonon branch in the vibrational spectrum (between points R and M of the Brillouin zone) with negative values of squares of frequencies. The condensation of soft mode R₅ at the boundary point of the Brillouin zone leads to rhombohedral distortion of the cubic structure with the unit cell volume doubling. The calculated frequencies at q=0 of the ScF₃ lattice in the distorted rhombohedral phase are real-valued; the number and position of frequencies active in Raman scattering are in accord with the experimental values.     

The cubic-to-monoclinic phase transition in (NH4)3ScF6 cryolite: A Raman scattering study

This paper reports on a Raman study of the cubic-to-monoclinic phase transition in (NH₄)₃ScF₆ cryolite. We observed sharp anomalies in the frequencies and half-widths of the Raman lines corresponding to internal vibrations of the ScF ₆ ³⁺ ions and to lattice vibrations; no soft lattice mode condensation was revealed. It is concluded that the phase transition studied is related primarily to the orientational ordering of these ions.     

A raman scattering study of the phase transition in the ammonium oxyfluoride (NH4)3TiOF5

Raman spectra of a polycrystalline sample of the perovskite-like oxyfluoride (NH₄)₃TiOF₅ are measured in the frequency region 100–3600 cm^?1 at temperatures ranging from 91 to 370 K under hydrostatic pressures of up to 9 GPa, which include the range of the phase transition from the orientationally disordered cubic phase to the low-symmetry phase. Anomalies in the spectral parameters due to the phase transition are revealed in the range of vibrations of TiOF₅ octahedral groups.     

Raman spectroscopic study of the phase transitions induced by hydrostatic pressure in a Rb2KScF6 crystal

The Raman spectra of Rb₂KScF₆ elpasolite crystals are studied in the pressure range up to 7 GPa. A phase transition is revealed at a pressure of approximately 1 GPa. Analysis of the changes in the spectral parameters shows that the phase transition is accompanied by a doubling of the volume of the primitive cell in the initial cubic phase. Judging from the character of the variations in the pressure dependences of the frequency of the observed vibrations, there can exist another transition to the phase with a lower symmetry at a pressure of approximately 2.1 GPa.     

Manifestations of Structural Phase Transitions in a Rb2KLuF6 Crystal in Its Raman Spectra

Optics and Spectroscopy - The Raman spectra of an Rb2KLuF6 crystal are studied in the temperature range from 8 to 375 K, which includes two phase transitions: one of which proceeds from a cubic to...     

Phase transition in the layered perovskite CsScF4 induced by hydrostatic pressure

Using polarization microscopy and Raman scattering, we have discovered a new phase transition in the layered perovskite crystal CsScF₄ under a hydrostatic pressure around 6 GPa. The proposed space group of the high-pressure phase is C _2h ² , Z=4. Fiz. Tverd. Tela (St. Petersburg) 41, 1683–1685 (September 1999)     

Magnetic properties, magnetoresistance, and Raman spectra of CuV x Cr1 − x S2

The results of investigations of the magnetic and Raman spectra, magnetic properties, and magnetoresistance of vanadium-substituted chromium copper disulfides CuV _x Cr_{1 ? x} S₂ (x = 0.1) are presented.