First-principles study of the effect of (111) strain on octahedral rotations and structural phases of LaAlO_3

摘要

The structural and electronic response of LaAlO_3 to biaxial strain in the (111) plane is studied by density functional theory (DFT) and compared with strain in the (001) plane and isostatic strain. For (111) strain, in-plane rotations are stabilized by compressive strain and out-of-plane rotations by tensile strain. This is an opposite splitting of the modes compared with (001) strain. Furthermore, for compressive (111) strain, in-plane rotations are degenerate with respect to the rotation axis, giving rise to Goldstone-like modes. We rationalize these changes in octahedral rotations by analyzing the V_A/V_B polyhedral volume ratios. Finally, we investigate how strain affects the calculated band gap, and find a 28% difference between the strain planes under 4% tension. This effect is attributed to different A-site dodecahedral crystal field splitting for (001) and (111) strains.