High-pressure phase of the cubic spinel

Abstract

It has been observed that the fcc spinel (Formula presented) transforms to a tetragonal structure at about 12 GPa. The tetragonal phase does not revert to the cubic phase upon decompression and its unit-cell constants at ambient pressure are (Formula presented) and (Formula presented) (distorted fcc). Within the experimental uncertainty, there is no volume change at the transition. The (Formula presented) ratio of the tetragonal spinel is almost independent of pressure and equal to 0.91. The phase transition is attributed to the Jahn-Teller-type distortion and the ionic configuration can be assumed as (Formula presented) The bulk modulus of the cubic phase is 206(4) GPa. © 1998 The American Physical Society.