High-pressure neutron powder diffraction study of the Im phase of ReO₃

The structure of ReO₃ has been studied over the pressure range from 1.27 to 8.01 GPa by neutron powder time-of-flight diffraction as well as by X-ray diffraction up to 41 GPa using Fluorinert as the pressure-transmitting medium. The cubic phase was found to be stable in the pressure range 0.5 to 13.2 GPa and to be highly compressible with a zero-pressure bulk modulus of B_o = 43 (1) GPa. The neutron data were used in least-squares refinements, showing that the ReO₆ octahedra remain almost undistorted, while the Re-O-Re bond angle decreases from 166.5 (1) to 146.4 (3)° within the investigated pressure range of 1.27 to 8.01 GPa. The compression mechanism is also described in terms of sphere-packing models of the oxygen anions.