S. N. Krylova

Hydrostatic Pressure-Induced Phase Transitions in Rb2KInF6 and Rb2KScF6 Crystals: Raman Spectra and Lattice Dynamics Simulations

Raman scattering spectra of Rb2KInF6 and Rb2KScF6 crystals have been studied under hydrostatic pressure up to 5.3 GPa at room temperature. Results are interpreted within semiempirical simulations of the lattice dynamics. Observed phase transitions both in Rb2KInF6 and Rb2KScF6 crystals are associated with condensation of soft F1g phonon mode. High-pressure phases for both crystals are supposed to be of C2/m space group.

A Raman Study of Hydrostatic Pressure Induced Phase Transitions in Rb 2 KInF 6 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 Flg mode. A probable high-pressure phase is the phase with space group C2/m.

Raman spectra and phase transitions in Rb2KInF6 elpasolite

The Raman spectra of Rb2KInF6 elpasolite crystal have been studied in a wide temperature range, including two phase transitions: from the cubic phase to the tetragonal phase and then to the monoclinic phase. Several anomalies of internal modes of InF6 octahedra and low-frequency lattice vibrations, which are related to the structural changes at the transition points, have been found and quantitatively analyzed. The results of a quantitative analysis of the temperature dependences of the parameters of spectral lines are in good agreement with the thermodynamic data on the phase transitions.

Raman Scattering Study of Temperature Phase Transitions in (NH4)3MoO3F3

Raman scattering spectra of (NH4)3MoO3F3 crystal have been studied in temperature range from 77 to 377 K. Parameters of Raman lines have been quantitatively analyzed. Transitional anomalies were found in the internal modes octahedral groups MоO3F3 and ammonium groups at 297 K. The ferroelectric phase transition (297 K) in (NH4)3MoO3F3 is associated with the partly ordering of octahedral MоO3F3 and the ammonium cations. The ferroelastic phase transition (205 K) is associated with the further ordering of octahedral MоO3F3.

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.

Vibrational spectrum and elastic properties of KPb2Cl5 crystals

The Raman spectra and elastic moduli of KPb2Cl5 crystals were studied experimentally. The results are interpreted using a parameter-free model of the crystal lattice dynamics with inclusion of the multipole moments of the electron shells of ions. The calculated and experimental results are in good agreement. It is shown that not only the halogen ions but also the heavy cations make a significant contribution to the eigenvectors of high-frequency lattice vibration modes, which accounts for the relatively low frequencies of these modes.

Raman Scattering Study Temperature Phase Transitions of Rb2KInF6 Crystal

Raman scattering spectra of Rb2KInF6 crystal have been studied in a wide temperature range, including two phase transitions: from cubic to tetragonal, and then – to the monoclinic phase. Hardening of soft phonon modes was observed that attributes them to the transitions of displacive type. Parameters of Raman lines have been quantitatively analyzed and found in good agreement with known thermodynamic characteristics of these transitions. No evidences of order – disorder processes were observed in the Raman spectra of the high-symmetry phase.

Pressure-Induced Phase Transitions in RbMnCl3 Crystal—Raman Spectra and Lattice Dynamics

Raman scattering spectra of RbMnCl 3 crystal has been studied at ambient conditions and under high hydrostatic pressure. Results are interpreted within abinitio lattice dynamics approach. Experimental results agree rather well with numerical simulations at the lower frequencies range, while a bit worse—for higher frequency modes. The first transition was observed at 0.7 GPa in good agreement with earlier measurements, and spectral transformation agrees with transition to the perovskite cubic phase predicted theoretically. New transitions were found at 1.1 GPa and 5 GPa, presumably—to distorted cubic phases.

Raman scattering and phase transitions in fluorides with elpasolite structure

ABSTRACT Raman scattering spectra of Rb2KHoF6 and Rb2KDyF6 crystals have been studied in temperature range from 20 K to 399 K and from 7 K to 500 K respectively. Raman spectra of Rb2KHoF6 crystal are distorted due to the fluorescence process. Parameters of Raman lines have been quantitatively analyzed. The investigation points to the considerable role of CX6 groups in the temperature phase transition in Rb2KHoF6 and Rb2KDyF6 crystals. The anomalies of spectra changes with temperature testify the first order phase transitions in these crystals.