The structural variation of rhombohedral LaAlO3 perovskite under non-hydrostatic stress fields in a diamond-anvil cell.

The structural variation of LaAlO(3) perovskite under non-hydrostatic stress developed in the pressure medium within a diamond-anvil cell was determined using single-crystal x-ray diffraction. The experimental results show that the lattice of LaAlO(3) becomes more distorted and deviates from the hydrostatic behavior as pressure is increased up to 7.5 GPa. The determination of the crystal structure further confirms that the octahedral AlO(6) groups become more distorted, but the octahedral rotation around the threefold axis decreases as under hydrostatic conditions. These experimental results can be reproduced from knowledge of the elastic tensor of the sample at ambient conditions and the stress state within the pressure medium. Further calculations for two other orientations also indicate that non-hydrostatic stress has only a small effect on the rotation of the AlO(6) octahedra towards zero, but non-hydrostatic stress inevitably leads to distortions in the crystal lattice and the AlO(6) octahedra. As a result, the crystal structure is eventually driven away from cubic symmetry under non-hydrostatic conditions, whereas it evolves towards cubic symmetry under hydrostatic pressure.