Showing papers by "Gong Li published in 2014"

Structure determination of the high-pressure phase of CdSe

Abstract: Structural phase transition sequence of CdSe has been investigated at pressures up to 60 GPa under quasi-hydrostatic conditions using synchrotron X-ray diffraction. A phase transition from the wurtzite type (B4) to the NaCl-type (B1) structure has been observed, followed by another phase transition to an orthorhombic structure at 27 GPa, in agreement with previous reports. We show that this high-pressure orthorhombic phase has a Pnma symmetry rather than being a Cmcm-symmetric structure as previously suggested. From our observations, the appearance of the new reflections and reflection splitting with increasing pressure is due to the change of atomic relative positions in crystal lattice and the difference in the compression ratio of lattice parameters for the Pnma structure, and we find no evidence for the third phase transition reported previously. The pressure-induced phase transition of CdSe has been further confirmed by the density-functional theory calculations.

Structures of two intermediate phases between the B1 and B2 phases of PbS under high pressure

Abstract: The structural transitions of PbS were investigated at pressures up to 50 GPa using synchrotron powder and single crystal X-ray diffraction (XRD) methods in diamond anvil cells. We found two intermediate phases between the B1 phase under atmospheric pressure and the B2 phase at 21.1 GPa, which is different to previous reports. The structures of these two intermediate phases were indexed as B27 and B33, respectively. Their structural parameters were investigated using density functional theory (DFT) calculations. Our results provide a new insight into understanding the transition pathway between the B1 and B2 phases in PbS.

Structure determination of the intermediate phase of PbSe using experiments and calculations

Abstract: 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.