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

Theoretical analysis based on the Landau-Ginzburg-Devonshire theory is used to show that the joint action of flexoelectric effect and rotostriction leads to a large spontaneous in-plane polarization (similar to 1-5 mu C/cm(2)) and pyroelectric coefficient (similar to 10(-3) C/m(2) K) 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. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3701152]