Pressure-induced phase transitions in nanocrystalline ReO₃

Abstract

Pressure-induced phase transitions in the nanocrystals of ReO₃ with an average diameter of ~12 nm have been investigated in detail by using synchrotron x-ray diffraction and the results compared with the literature data of bulk samples of ReO₃. The study shows that the ambient-pressure cubic I phase (space group Pm3̅m ) transforms to a monoclinic phase (space group C 2/c), then to a rhombohedral I phase (space group R3̅c ), and finally to another rhombohedral phase (rhombohedral II, space group R3̅c ) with increasing pressure over the 0.0-20.3 GPa range. The cubic I to monoclinic transition is associated with the largest volume change (~5%), indicative of a reconstructive transition. The transition pressures are generally lower than those known for bulk ReO₃. The cubic II (Im3̅) or tetragonal (P4/mbm) phases do not occur at lower pressures. The nanocrystals are found to be more compressible than bulk ReO₃. On decompression to ambient pressure, the structure does not revert back to the cubic I structure.