Structure determination of the intermediate phase of PbSe using experiments and calculations
The pressure-induced structure transitions of PbSe were investigated at pressures up to 50 GPa in diamond anvil cells using synchrotron powder and single-crystal X-ray diffraction methods. A phase transition from the initial NaCl-type structure to an intermediate phase was observed at 4.8 GPa, followed by another phase transition to a CsCl-type structure at 19.5 GPa, which is in agreement with previous reports. In addition, the NaCl-type, Pnma, Cmcm, and CsCl-type structures of PbSe were investigated using density functional theory calculations. Based on the experiments and calculations, the intermediate phase has Pnma symmetry rather than Cmcm symmetry, as has been previously suggested. Some of the diffraction peaks of the Pnma phase were broad in the high-pressure experiments, but were determined to be single diffraction peaks rather than the overlap of multiple peaks by different experimental methods. The Pnma and Cmcm structures of PbSe were compared. It was found that two structures were very similar, and it was difficult to distinguish one power diffraction pattern from the other.