Phase transformation in Sm2O3 at high pressure: In situ synchrotron X-ray diffraction study and ab initio DFT calculation

Sm2O3 was compressed at room temperature up to 44.0 GPa and then decompressed back to ambient pressure. In situ X-ray diffraction was used to monitor the structural changes in the sample. A cubic to hexagonal phase transformation was observed in Sm2O3 for the first time. After decompression back to ambient pressure, the hexagonal phase was not quenchable and transformed to a monoclinic phase. Ab initio Density- Functional-Theory (DFT) calculations were performed to obtain theoretical data for comparison with the experimental results and elucidation of the transformation mechanism. A possible phase transformation mechanism that is consistent with the experimental results and theoretical calculations is proposed.