Aleksandr S. Oreshonkov

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.

Raman scattering study of δ-BiB3O6 crystal

ABSTRACT The total set of polarized Raman spectra have been obtained at room temperature, and an assignment of observed modes based on the lattice dynamics simulation and polarization selection rules is proposed. An LO-TO splitting of A1 Raman bands have been observed.

Vibrational spectra of NdF3 crystal

ABSTRACT The vibrational spectroscopy investigation of phase transitions in NdF3 crystal is reported. Spectra were obtained in temperature range from 300 to 10 K. It has been shown that, down to 10 K, the trigonal tysonite structure of NdF3 trifluoride remains stable.

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.

Anisotropic crystal of the δ-BiB3O6 investigated by vibrational spectroscopy

The vibrational spectroscopy has been applied to investigate the structure the BiB3O6 (BIBO) crystal. Based on the experimental results, the total set of phonons mode of the polarized Raman spectra was proposed. To verify the obtained experimental data have been performed theoretical calculation in software package LADY.

Structure, Thermal Stability, and Spectroscopic Properties of Triclinic Double Sulfate AgEu(SO4)2 with Isolated SO4 Groups

Silver-europium double sulfate AgEu(SO4)2 was obtained by solid-phase reaction between Ag2SO4 and Eu2(SO4)3. The crystal structure of AgEu(SO4)2 was determined by Monte Carlo method with simulated annealing, and after that, it was refined by the Rietveld method from X-ray powder diffraction data. The compound crystallizes in the triclinic symmetry, space group P1̅ ( a = 0.632929(4), b = 0.690705(4), c = 0.705467(4) nm, α = 98.9614(4), β = 84.5501(4), γ = 88.8201(4)°, V = 0.303069(3) nm3). Two types of sulfate tetrahedra were found in the structure, which significantly affects the spectroscopic properties in the IR-range. In the temperature range of 143-703 K, the average linear thermal expansion coefficients of cell parameters a, b, and c are very similar, (1.11-1.67) × 10-5 K-1 in magnitude, and therefore, AgEu(SO4)2 expands almost isotropically. Upon heating in argon flow, AgEu(SO4)2 is stable up to 1053 K. The luminescence spectra in the region of ultranarrow 5D0-7F0 transition contain a single narrow and symmetric line at 579.5 nm that is evidence of good crystalline quality of AgEu(SO4)2 and uniform local environment of Eu3+ ions in the structure. Distribution of luminescence bands is determined by the environment of Eu3+ ions in the structure. Influence of Ag+ ions on the electron density distribution at Eu sites is detected.

Raman Spectra and Structural Phase Transition in Pr3Sb5O12 Crystal

Raman spectroscopy investigation of phase transition in Pr3Sb5O12 crystal is reported. Spectra were obtained in temperature range from 300 to 800 K. Soft mode restoration has been found below 735 K, that allows to attribute structural phase transition as displacive.