Surface polar states and pyroelectricity in ferroelastics induced by flexo-roto field

TL;DR

This paper theoretically demonstrates that the combined flexoelectric and rotostriction effects induce significant surface polar states and pyroelectricity in non-ferroelectric ferroelastics like SrTiO3 through a flexo-roto field.

Contribution

It introduces the concept of the flexo-roto field and shows its role in generating surface polarization and pyroelectricity in ferroelastics with octahedral rotations.

Findings

Large in-plane polarization (~1-5 μC/cm²) near surfaces.

Pyroelectric coefficient (~10^-3 C/m²K) induced by flexo-roto field.

Flexo-roto field exists at surfaces and interfaces in materials with octahedral rotations.

Abstract

Theoretical analysis based on the Landau-Ginzburg-Devonshire (LGD) theory is used to show that the joint action of flexoelectric effect and rotostriction leads to a large spontaneous in-plane polarization (~ 1-5 muC/cm2) and pyroelectric coefficient (~10^-3 C/m2K) in the vicinity of surfaces of otherwise non-ferroelectric ferroelastics, such as SrTiO3, with static octahedral rotations. The origin of the improper polarization and pyroelectricity is an electric field we name flexo-roto field whose strength is proportional to the convolution of the flexoelectric and rotostriction tensors with octahedral tilts and their gradients. Flexo-roto field should exist at surfaces and interfaces in all structures with static octahedral rotations, and thus it can induce surface polar states and pyroelectricity in a large class of otherwise nonpolar materials.