Journal
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS
Volume 94, Issue 5, Pages 977-984Publisher
AMER INST PHYSICS
DOI: 10.1134/1.1484991
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New 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 R (3) over barc 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 R-5 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. (C) 2002 MAIK Nauka/Interperiodica.
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