Structural Phase Transitions of Ga2Se3 and GaSe under High Pressure

High pressure X-ray powder diffraction studies have been made on α-Ga2Se3 up to 27 GPa andε-GaSe up to 64 GPa by using synchrotron radiation. A structural phase transition is observed for α-Ga2Se3 at 14 GPa, as is observed in β-Ga2Se3. The diffraction patterns of the high pressure phases of α- and β-Ga2Se3 are almost the same, showing that the structures of the high pressure phases of both α- and β-Ga2Se3 are the same. On the other hand, the structural phase transition for ε-GaSe is observed near 25 GPa. The diffraction pattern of the high pressure phase of GaSe is similar to that of Ga2Se3. This shows that the high pressure phase of GaSe is similar to that of Ga2Se3, although the atomic concentrations in the alloys are different between Ga2Se3 and GaSe. Most of the diffraction profile of the high pressure phase is explained by a NaCl type structural model, suggesting that the high pressure phase has a structure similar to NaCl.