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\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \bar 3 $$\end{document}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.