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.
@article{arxiv.1201.5085,
title = {Surface polar states and pyroelectricity in ferroelastics induced by flexo-roto field},
author = {A. N. Morozovska and E. A. Eliseev and S. V. Kalinin and Long Qing Chen and Venkatraman Gopalan},
journal= {arXiv preprint arXiv:1201.5085},
year = {2015}
}