The structural variation of rhombohedralLaAlO3 perovskite under non-hydrostatic stress fields in a diamond-anvil cell

Abstract

The structural variation of LaAlO3 perovskite under non-hydrostatic stress developed in the pressure medium within a diamond-anvil cellwas determined using single-crystal x-ray diffraction. The experimental results show that the latticeof LaAlO3 becomes more distorted and deviates from the hydrostatic behavior as pressure is increased upto 7.5 GPa. The determination of the crystal structure further confirms that the octahedralAlO6 groups become more distorted, but the octahedral rotation around the threefold axisdecreases as under hydrostatic conditions. These experimental results can be reproducedfrom knowledge of the elastic tensor of the sample at ambient conditions and the stressstate within the pressure medium. Further calculations for two other orientations alsoindicate that non-hydrostatic stress has only a small effect on the rotation of theAlO6 octahedra towards zero, but non-hydrostatic stress inevitably leads to distortions in the crystal lattice andthe AlO6 octahedra. As a result, the crystal structure is eventually driven away from cubic symmetryunder non-hydrostatic conditions, whereas it evolves towards cubic symmetry underhydrostatic pressure.