Pressure-induced structural phase transition in ReO3

We have investigated the pressure-induced structural phase transition in ReO3 by neutron diffraction on a single crystal. We collected neutron diffraction intensities from the ambient and high pressure phases at P = 7 kbar and refined the crystal structures. We have determined the stability of the high pressure phase as a function temperature down to T = 2 K and have constructed the (P-T) phase diagram. The critical pressure is P, = 5.2 kbar at T = 300 K and decreases almost linearly with decreasing temperature to become P-c = 2.5 kbar at T= 50 K. The phase transition is driven by the softening of the M-3 phonon mode. The high pressure phase is formed by the rigid rotation of almost undistorted ReO6 octahedra and the Re-O-Re angle deviates from 180 degrees. We do not see any evidence for the existence of the tetragonal (P4/mbm) intermediate pressure phase reported earlier. (c) 2006 Elsevier Ltd. All rights reserved.