Phase transitions in ReO3 studied by high-pressure X-ray diffraction

ReO3 has been studied at pressures up to 52 GPa by X-ray powder diffraction. The previously observed cubic Im (3) over bar high-pressure phase was shown to transform to a monoclinic MnF3-related phase at about 3 GPa. All patterns recorded above 12 GPa could be indexed on rhombohedral cells. The compressibility was observed to decrease abruptly at 38 GPa. It is therefore proposed that the oxygen ions are hexagonally close packed above this pressure, giving rise to two rhombohedral phases labelled I and II. The zero-pressure bulk moduli B-0 of the observed phases were determined and the rhombohedral phase II was found to have an extremely large value of 617(10) GPa. It was found that ReO3 transforms back to the Pm (3) over bar m phase found at ambient pressure. (C) 2000 International Union of Crystallography Printed in Great Britain - all rights reserved.