XAFS STUDY OF REO3 UNDER PRESSURE

We have measured the XAFS of the Re L(m)-edge in ReO3 through and above its compressibility collapse transition occurring at 5 kbar, during which the ReO6 octahedra begin to undergo collective rotational displacements. The FEFF program of Rehr et al. allows for very good fits to the data, and the rotation angles obtained are in accord - within our ability to determine sample pressures - with those determined by Jorgensen et al. using neutron diffraction. We have also found that an ABA atomic bridge, in which the atom B vibrates perpendicularly and symmetrically about a position collinear with both A atoms, gives an XAFS contribution identical to that of a static displacement of the atom B.