K. S. Aleksandrov

Structure transformations during phase transitions in the K3WO3F3 oxyfluoride

AbstractThe structures of three phases of the K3WO3F3 crystal have been determined from X-ray diffraction data obtained for a powder sample. The profile and structural parameters have been refined according to the technique implemented in the DDM program. The results obtained have been discussed using the group-theoretical analysis of the complete order parameter condensate, which takes into account the critical and noncritical atomic displacements and allows the interpretation of the experimental data. The sequence of structural transformations is found to be as follows:

Pressure-induced phase transition in the cubic ScF3 crystal

Fm\bar 3m\xrightarrow[{(\eta _1 ,0,0)}]{{11 - 10(\Gamma _4^ - )}}I4mm\xrightarrow[{(\eta _1 ,\eta _2 ,0)}]{{11 - 10(\Gamma _4^ - )}}Cm

Structures of distorted phases and critical and noncritical atomic displacements of elpasolite Rb2KInF6 during phase transitions

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Electromechanical properties and anisotropy of acoustic wave propagation in CuB2O4 copper metaborate

AbstractNew phase transitions induced by hydrostatic pressure in a cubic (under standard conditions) ScF3 crystal are discovered by the methods of polarization microscopy and Raman scattering. The space groups

Acoustical and acoustooptical properties of lead tetraborate single crystals

R\bar 3c

Phase transition in the layered perovskite CsScF4 induced by hydrostatic pressure

for Z=2 and Pnma for Z=4 are proposed for the high-pressure phases. A nonempirical computation of the lattice dynamics of the crystal is carried out. It is shown that, under normal pressure, the cubic phase is stable down to T=0 K, while the application of a hydrostatic pressure gives rise to a phonon branch in the vibrational spectrum (between points R and M of the Brillouin zone) with negative values of squares of frequencies. The condensation of soft mode R5 at the boundary point of the Brillouin zone leads to rhombohedral distortion of the cubic structure with the unit cell volume doubling. The calculated frequencies at q=0 of the ScF3 lattice in the distorted rhombohedral phase are real-valued; the number and position of frequencies active in Raman scattering are in accord with the experimental values.