A. S. Krylov

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 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 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.

Low-temperature features of Raman spectra below magnetic transitions in multiferroic Ho1–xNdxFe3(BO3)4 and Sm1–yLayFe3(BO3)4 single crystals

ABSTRACT Raman spectra changes in multiferroic Ho1–xNdxFe3(BO3)4 (x = 0, 0.25, 0.5, 0.75) and Sm1–yLayFe3(BO3)4 (y = 0, 0.75) single crystals at low temperatures have been analyzed. The anomalies corresponding to the phase transition of the second order have been detected at the temperatures of magnetic phase transitions, being consistent with previously reported results of the magnetization study. A number of anomalies in the temperature dependences of the spectral lines associated with the occurrence of magnetic order. A mode corresponding to two-magnon scattering was revealed. Comparison of the features of low-temperature low-frequency spectra of solid solutions Ho-Nd and Sm-La has been carried out.

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 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 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.

Lattice Dynamics of Oxyfluoride Rb2KMoO3F3

The complete Raman spectra of oxyfluoride Rb2KMoO3F3 were obtained. At T ≈ 185 K phase transitions were found. Lattice dynamics of disordered structures of the investigated compound was simulated, and “soft” vibrational modes were found in the calculated spectrum.