Cation order-disorder phase transitions in LiGaO₂: Observation of the pathways of ternary wurtzite under high pressure

Two new high-pressure phases of LiGaO₂ have been discovered by direct compression of orthorhombic wurtzite-type LiGaO₂ at pressures between 7 and 22 GPa and the temperatures of 25-2000 °C by means of the multianvil apparatus. The new intermediate phase recovered above 13 GPa at room temperature has been determined as a cation-disordered tetragonal structure with lattice parameters a=0.287 63 (36) nm and c=0.419 29 (117) nm, space group I4/m. The new high-pressure phase recovered above 16 GPa and 1400 °C has been refined as a cation-disordered cubic structure with lattice parameter of a=0.411 34 (16) nm, space group Fm-3m. Powder x-ray diffraction and Raman scattering spectra observations reveal that besides the previously described polymorphic hexagonal phase, the tetragonal and cubic new phases of LiGaO ₂ are found to have rocksalt-related structures. Their structures can be labeled as layered-rocksalt-type, deformed-rocksalt-type, and disordered-rocksalt-type, respectively. The relationships between polymorphs of LiGaO₂ provide some new insights into the pathways of ternary wurtzite-type semiconductors under high pressure.