Experimental Observation of Possible Pressure-Induced Phase Transformation in GdAlO3 Perovskite Using In Situ X-ray Diffraction

Gadolinium aluminate perovskite (GdAlO3) was studied at high pressures of up to 23 GPa in a diamond anvil cell (DAC) using monochromatic synchrotron X-ray powder diffraction. Evidence of a pressure-induced phase transformation from orthorhombic (Pbnm) to rhombohedral (R3¯c) structure was observed at 21 GPa and further proved by DFT calculations. Before phase transition, the volumetric ratio of polyhedron A and B (i.e., VA/VB for ABX3 general notation) in the Pbnm phase continuously increased towards the ideal value of five at the transition, indicating a pressure-induced decrease in the structural distortion as opposed to the trend in many other orthorhombic perovskites (e.g., CaSnO3, CaGeO3, MgSiO3 and NaMgF3). Pressure–volume data of the Pbnm phase were fitted to the third-order Birch–Murnaghan equation of state yielding a bulk modulus (Ko) of 216 ± 7 GPa with a pressure derivative of the bulk modulus (Ko′) of 5.8 GPa (fixed). This work confirms the pressure-induced phase transformation from orthorhombic to a higher symmetry structure previously predicted in GdAlO3 perovskite.