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 R (3) c (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.