Behavior of CaBSiO4(OH) datolite at high temperatures and pressures of a water medium

Bulletin of the Russian Academy of Sciences: Physics - The behavior of CaBSiO4(OH) datolite compressed in a water medium at simultaneous high temperatures and pressures corresponding to the cold...     

Structure and lattice dynamics of the high-pressure phase in the ScF3 crystal

The high-pressure phase of the ScF₃ crystal has been studied using synchrotron radiation diffraction and Raman scattering. This phase existing in the pressure range 0.6–3.2 GPa is optically anisotropic: its structure is described by space group R $ \bar 3 $ \bar 3 c, Z = 2, and the transition is associated with the rotation of ScF6 octahedra around the threefold axis. The pressure dependences of the lattice parameters and the rotation angle have been determined. The number of lines in the Raman spectrum corresponds to the expected number for this structure; the recovery of soft modes has been observed above the phase transition.     

Raman spectroscopic study of the phase transitions in the (NH4)3WO3F3 oxyfluoride

The Raman spectra of (NH₄)₃WO₃F₃ perovskite-like oxyfluorides are measured in the frequency range 70–3600 cm^?1. The anomalies observed in the spectral parameters upon phase transitions at a temperature of 200 K under atmospheric pressure and at room temperature under a pressure of 1.4 GPa are interpreted.     

Raman spectra and phase composition of MnGeO3 crystals

MnGeO₃ single‐crystal samples have been synthesized by optical zonal melting and spontaneous crystallization. X‐ray crystal analysis showed the first sample to be a two‐phase one with phase ratio as follows: 17% – monoclinic C2/c, and 83% – orthorhombic Pbca; the phase ratio of the second sample was unknown. Raman spectra have been produced for these samples. Lattice dynamics has been simulated and polarization dependencies of lines' intensities have been analyzed to interpret experimental Raman spectra and to attribute lines to the spectra of monoclinic and orthorhombic phases. Copyright © 2015 John Wiley & Sons, Ltd.     

Behavior of natrolite zeolite and fluorapatite at high pressures in a water medium

The hysteresises (～0.3–0.4 GPa) of two transitions in natrolite at 0.9 and 1.45 GPa, considerable changes in the Raman spectra, and the appearance of very intense low-frequency mode at 75 cm^?1 in the overhydrated phase of high pressure of water medium up to 6.2 GPa are observed for the first time. The dependences of the band frequencies of this phase are nonlinear, due clearly to changes in the positions of H₂O in the channels. According to Raman data, fluorapatite placed together with natrolite in a water medium in a diamond anvil cell exhibits no transitions up to 6.2 GPa and displays linear pressure dependences of the band frequencies.     

Raman spectra and phase transitions in Rb<Subscript>2</Subscript>KInF<Subscript>6</Subscript> 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.     

Structural transformations in a single‐crystal Rb2NaYF6: Raman scattering study

This paper reports Raman spectroscopy investigation of phase transitions in Rb₂NaYF₆ crystal. The experimental spectra were compared with the calculated one. The spectra were obtained in temperature range from 8 to 300 K. The Raman spectra shows anomalous temperature‐dependent behavior at T₁ = 154 and T₂ = 122 K. Soft mode restoration has been found, which allows us to attribute first transition at 154 K to displacive type. Detailed analysis temperature dependencies of the line positions and widths have been performed. We found no effects of possible lattice disorder anywhere, except narrow (about 20 K) range above the T₁ temperature. The Raman spectra of Rb₂NaYF₆ crystal have been obtained and analyzed under hydrostatic pressure up to 4.33 GPa (at T = 295 K). The high pressure experiment up to 4.33 GPa did not disclose any effects associated with phase transitions. The lattice vibration spectra were calculated up to 10 GPa. The calculation has been demonstrated that the Rb₂NaYF₆ does not undergo high pressure phase transition. Copyright © 2013 John Wiley & Sons, Ltd.     

In situ Raman study of wairakite and dawsonite interaction with water at high <Emphasis Type="Italic">P</Emphasis>–<Emphasis Type="Italic">T</Emphasis> parameters

The behavior of wairakite CaAl₂Si₄O₁₂ · 2H₂O and dawsonite NaAlCO₃(OH)₂ in a water medium is studied by means of in situ Raman spectroscopy at the simultaneously high temperatures and pressures (up to T = 723 K and P = 1 GPa). After the initial minerals are partially dissolved, phillipsite forms in the wairakite–water system, and a glass-like phase is generated in the dawsonite–water system. These minerals show no signs of overhydration. The amorphization of the wairakite structure that occurs at high temperatures and pressures was reversible.     

Anomalous Raman phenomenon of CuCrS2

Structural dynamics of the layered CuCrS₂ is investigated for the first time by using the Raman scattering method in 78–295 K temperature range on the samples synthesized by different methods. The Raman and IR spectra of CuCrS₂ were simulated within the valence force field model with the LADY program. The results presented indicate that the lattice dynamics of CuCrS₂ depends strongly on the real microstructure and technology of the sample preparation. The anomalous splitting of the A₁ phonon mode might be due to presence of the α‐ and β‐domains. Copyright © 2010 John Wiley & Sons, Ltd.     

Soft-mode condensation in Raman spectra of the Rb2KScF6 elpasolite

This paper reports on the first observation of soft-mode condensation in the Raman spectra of the Rb₂KScF₆ elpasolite crystal below the transition points from the cubic to tetragonal and, subsequently, monoclinic phase.