Structural phases of strained LaAlO3 driven by octahedral tilt instabilities

TL;DR

This study uses first-principles calculations to explore how epitaxial strain influences structural phase transitions and octahedral tilt patterns in LaAlO3, revealing tunable tilt axes and potential for selective stabilization.

Contribution

It demonstrates the strain-induced evolution of octahedral tilt patterns and axes in LaAlO3, providing insights into structural control via epitaxial strain and relaxation mechanisms.

Findings

Strain induces phase transitions with distinct octahedral tilting patterns.

Tilt axis changes from out-of-plane to in-plane with strain.

Uniaxial relaxation can stabilize different tilt configurations.

Abstract

We investigate the effect of epitaxial strain on [001]-oriented LaAlO3 using first-principles density functional calculations. We find a series of structural phase transitions between states characterized by distinct patterns of tilting of the AlO6 octahedra. By tuning the biaxial strain from compressive to tensile, we induce an evolution in the crystal structure in which the tilt axis changes from out-of-plane to in-plane, corresponding to space groups I4/mcm and Imma. We also study the effect of uniaxial relaxation of the usual biaxial epitaxial constraint and explore this as a mechanism for selectively stabilizing different patterns of octahedral tilts.