Structural phase transitions of cubic Gd2O3 at high pressures

Structural phase transitions of cubic Gd2O3 at high pressures


ABSTRACT

An irreversible structural transformation from the cubic phase to a hexagonal high-pressure phase was verified in Gd2O3 between 7.0 and 15 GPa. The compressibility and bond distances of both phases were determined by the refinement of the x-ray diffraction data. The high-pressure phase of Gd2O3 is 9.2% denser than the cubic phase at 7 GPa. After release of pressure, the high-pressure phase transformed to a monoclinic structure. The pressure-induced phase transition from the monoclinic to the hexagonal phase is reversible. Unlike the case at atmospheric pressure, the hexagonal phase was found to transform to the monoclinic phase by increase of temperature at high pressures. The lattice potential energies and electronic density of states of the cubic, monoclinic, and hexagonal high-pressure phases of Gd2O3 were calculated from the known structural models with density-functional method. The observed phase stability, transition pressure, and volume change are well explained by theoretical calculations.


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