Polarization Enhancement in Perovskite Superlattices by Oxygen Octahedral Tilts

TL;DR

This study reveals that interface-induced oxygen octahedral tilts in BaTiO3/CaTiO3 superlattices significantly enhance electric polarization, surpassing bulk BaTiO3, through a combination of genetic algorithms and density functional theory.

Contribution

The paper introduces a novel mechanism for polarization enhancement via oxygen octahedral tilts and predicts ground states with large polarization using advanced computational methods.

Findings

Enhanced polarization in superlattices exceeds bulk BaTiO3 values.

Oxygen octahedral tilts reduce oxygen octahedron rotation, boosting polarization.

Predicted ground states adopt Pc symmetry with large polarization values.

Abstract

Interface engineering in perovskite oxide superlattices has developed into a flourishing field, enabling not only further tuning of the exceptional properties, but also giving access to emergent physical phenomena. Here, we reveal a new mechanism for enhancing the electric polarization by the interface-induced oxygen octahedral tilts in BaTiO3/CaTiO3 superlattices. By combining a novel genetic algorithm with density functional theory (DFT), we predict that the true ground states in 1:1 and 2:2 BaTiO3/CaTiO3 superlattices grown on SrTiO3 adopt Pc symmetry with a large proper electric polarization (32.8{\mu}C/cm2 for 1:1 and 35.8 {\mu}C/cm2 for 2:2 superlattices), which is even larger than that of bulk BaTiO3. The tilt of oxygen octahedron is found to play a key role for the enhancement of out-of-plane polarization in 1:1 superlattices because it reduces greatly the rotation of oxygen octahedron (out-of-phase) which significantly suppresses the out-of-plane polarization.