PRESSURE X-RAY DIFFRACTION STUDY OF PHASE TRANSITIONS IN ReO3
J.-E. Jorgensen1, J. Staun Olsen2, and L. Gerward3
1Dept. Chemistry,
University of Aarhus, DK-8000 Aarhus C, Denmark,
2Physics Laboratory, H. C. —rsteds
Institute, University of Copenhagen, Universitetsparken 5,
Copenhagen, Denmark,
3Laboratory for Applied Physics,
Technical University of Denmark, Building 307, DK-2800 Lyngby,
Denmark.
jenserik@kemi.aau.dk
Keywords: High pressure diffraction and phase transitions.
ReO3 has been studied in the pressure range 0 to 50 GPa by energy dispersive X-ray powder diffraction using synchrotron radiation and a diamond anvil cell. Phase transitions were observed at 3 and 12 GPa and the structure was found to be cubic below 3 GPa. ReO3 crystalises in space group Pm3_m at ambient pressure and earlier neutron diffraction studies have shown that the structure is tetragonal (P4/mbm) at 0.52 GPa and cubic (Im3_) in the pressure range 0.73 to 2.74 GPa [1].
A new monoclinic phase was observed in the pressure range 3 to 12 GPa. The crystal structure of this phase is presumably related to the MnF3 structure (C2/c) although one reflection violating C-centering is observed. The limited resolution prevent a determination of the space group of the new phase. Above 12 GPa a trigonal VF3 (R3_c) phase was observed in agreement with earlier work [2]. The volume per formula unit changes discontinuously and is reduced by about 4.7% in the cubic to monoclinic transition at 3 GPa while no discontinuity is observed in the monoclinic to trigonal transition at 12 GPa.
The ReO6 octahedra in ReO3 are rotated during compression and it has been shown that the octahedra are undistorted up to 2.74 GPa [1].
The observed transition to the MnF3 like phase implies a distortion of the octahedra which is also the case in the VF3 phase.