Raman scattering study of temperature and hydrostatic pressure phase transitions in Rb₂KTiOF₅ crystal

Abstract

Raman spectra of Rb2KTiOF5 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 TiOF5 pseudo‐octahedron. To interpret effects of lattice ordering, phonon spectra of several ordered phases of Rb2KTiOF5 were calculated within ab initio generalized Gordon–Kim model, and ordering of TiOF5 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. Copyright © 2011 John Wiley & Sons, Ltd.

Perovskite-like K3TiOF5 Exhibits (3 + 1)-Dimensional Commensurate Structure Induced by Octahedrally Coordinated Potassium Ions

“…The experimental Raman spectrum of K 3 TiOF 5 at room temperature further supports the existence of short-range anion order within the [TiOF 5 ] 3– units (Figure b). The intense line at the frequency of ν 1 (899 cm –1 ) is consistent with the Ti–O stretching vibration of the [TiOF 5 ] 3– unit observed in related oxyfluorides. , In addition, the lines of the Ti–F stretching and bending vibrations of the moiety occur at low frequencies (ν 2 = 519 cm –1 , ν 3 = 479 cm –1 , ν 4 = 326 cm –1 , ν 5 = 283 cm –1 , and ν 6 = 167 cm –1 ).…”

Raman spectroscopic study of the lattice dynamics in the Rb2KMoO3F3 oxyfluoride

“…Depending on the ratio of the ionic radii R A and R A' and also on the type of M atoms, the structure can be distorted as a result of two [7][8][9][10][11][12][13][14][15] or one phase transition [1,7,[11][12][13][14]16], or it can remain stable down to the liquid helium temperature [7,[11][12][13][14]. For instance, despite very close values of the ionic radii of Mo (R Mo = 0.073 nm) and W (R W = 0.074 nm) atoms, the Rb 2 KMoO 3 F 3 elpasolite undergoes a phase transition on cooling [17], while the Rb 2 KWO 3 F 3 elpasolite remains cubic and does not undergo any phase transformations.…”

Recent advances in linear and nonlinear Raman spectroscopy. Part VII

“…studied using Raman spectroscopy the amorphous to crystalline transformation in Ta 2 O 5 , a strategic material for current and future applications in microelectronics and optics . Krylov and co‐workers used Raman scattering to study temperature and hydrostatic pressure phase transitions in Rb 2 KTiOF 5 crystal . Lin and Cheng described the use of hot‐stage microscopy and thermal MRS in the study of phase transformation of metoclopramide HCl monohydrate .…”