The Phase Transition of Eu₂O₃ under High Pressures

Pressure-induced phase transition of cubic Eu₂O₃ is studied by angle-dispersive x-ray diffraction (ADXD) up to 42.3GPa at room temperature. A structural transformation from a cubic phase to a hexagonal phase is observed, which starts at 5.0GPa and finishes at about 13.1GPa. The phase transition leads to a volume collapse of 9.0% at 8.6GPa. The hexagonal phase of Eu₂O₃ maintains stable up to the highest experiment pressure. After release of pressure, the high-pressure phase transforms to a monoclinic phase. The pressure-volume data are fitted with the Birch-Murnaghan equation of state. The bulk moduli obtained upon compression from the fitting are 145(2)GPa and 151(6)GPa for the cubic and hexagonal phases, respectively, when their first pressure derivatives are fixed at 4.