A. Yu. Likhacheva

Pressure-induced phase transition in the cubic ScF3 crystal

Pressure-induced phase transitions in the ScF3 crystal were studied using synchrotron radiation diffraction, polarization microscopy, and Raman spectroscopy. The phase existing in the range 0.6–3.0 GPa is optically anisotropic; its structure is described by space group R3c (Z = 2), and the transition is due to rotation of ScF6 octahedra around a threefold axis. The pressure dependence of the structural parameters and angle of rotation are determined. The number of Raman spectral lines corresponds to that expected for this structure; above the phase transition point, a recovery of soft modes takes place. At a pressure of 3.0 GPa, a transition occurs to a new phase, which remains metastable as the pressure decreases. The results are interpreted using an ab initio method based on the Gordon-Kim approach.

Structure of the intermediate high-pressure phases of ternary lead tellurides

In chambers with diamond anvils, the structure of high-pressure phases of ternary lead tellurides Pb1−xSnxTe (x = 0.29) and Pb1−xMnxTe (x = 0.05) and nonstoichiometric crystals Pb0.55Te0.45, Pb0.45Te0.55 is analyzed by the synchrotron radiation diffraction method at pressures of P up to 14 GPa. The orthorhombic structure of the intermediate high-pressure phase (space group Pnma) is determined for all the samples above 6 GPa. Models of the phase transition in PbTe from the initial rock salt structure to the orthorhombic phase, which constitutes a distorted variant of NaCl, as well as the properties of this phase, are discussed.

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

AbstractThe 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

The deformation mechanism of a pressure-induced phase transition in dehydrated analcime

\bar 3

Structural evolution of Li-exchaned natrolite at pressure-induced over-hydration: An X-ray diffraction study

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.

In situ Raman study of wairakite and dawsonite interaction with water at high P–T parameters

The intermediate phases preceding overhydration are observed by Raman spectroscopy both in scolecite Ca[Al2Si3O10] · 3H2O and in thomsonite NaCa2[Al5Si5O20] · 6H2O upon compression in an aqueous medium. The first intermediate phase of scolecite is attributed to a phase precursor revealed earlier using XRD at pressure of ∼1 GPa. The widening of the Raman bands of O-H vibrations caused by the disordering of H2O, which appears after additional water molecules are embedded in the zeolite channels, is typical of this intermediate phase. It is assumed on the basis of the Raman spectroscopy data that scolecite contains second overhydrated and second intermediate phases.

The application of in situ X-ray diffraction for the study of mineral reactions: The formation of lawsonite at 400°C and 25 kbar

Abstract The elastic and structural behaviour of dehydrated analcime in compression in a non-penetrating medium up to 3 GPa was studied in a diamond anvil cell using in situ synchrotron powder diffraction. A first-order phase transition at 0.4-0.7 GPa is accompanied by a symmetry change from monoclinic (I2/a) to pseudo-rhombohedral (R3) due to trigonalization of the aluminosilicate framework. This is due to the migration of cations to new positions close to the 6-membered rings forming the channels. The reduction of the mean aperture of the structure-forming 6- and 8-membered rings, as a result of tetrahedral tilting, leads to a 7.5% reduction in volume at the phase transition. The bulk modulus values are 38(2) GPa for the low pressure (LP) phase [fitted with a Murnaghan equation of state, Kʹ = 4 (fixed)] and 11(4) GPa for the high pressure (HP) phase [fitted with a third-order Birch-Mumaghan equation of state, Kʹ = 9(1)]. The elastic behaviour of the LP phase is anisotropic, with compressibilities βa:βb:βc in the ratio 1:4:2; the most compressible direction b coinciding with the orientation of empty 8-membered rings. The compressibility of the HP phase is isotropic. Trigonalization appears to be the most effective (and probably unique) mechanism of radical volume contraction for the ANA structure type.

Powder diffraction and Raman spectroscopic study of lawsonite at high water pressure

The work is devoted to the experimental study of coronene C24H12 at high pressure and room temperature using in situ X-ray diffraction in a diamond anvil cell. The high-pressure phase P2/m of coronene was found at 0.9 GPa, the PV-equation of state for P2/m coronene phase was defined to 4 GPa: K0 = 10.8(3) GPa, K0′ = 7. At 5.9 GPa partial amorphization of coronene was observed. After the decompression to ambient pressure the high-pressure phase P2/m was preserved, that can be related with partial amorphization.