Strain gradient induced polarization in SrTiO3 single crystals

TL;DR

This study investigates how strain gradients induce polarization in SrTiO3 crystals, revealing significant flexoelectric effects, temperature and orientation dependence, and potential polar domain walls, expanding understanding of electromechanical coupling in centrosymmetric materials.

Contribution

It provides the first comprehensive measurements of the flexoelectric tensor in SrTiO3 and suggests local polarization can surpass ferroelectric levels, with implications for functional material design.

Findings

Strain-gradient-induced polarization varies with temperature and orientation.

Flexoelectric tensor components were quantitatively estimated.

Polarization around defects may exceed ferroelectric polarization.

Abstract

Piezoelectricity is inherent only in noncentrosymmetric materials, but a piezoelectric response can also be obtained in centrosymmetric crystals if subjected to inhomogeneous deformation. This phenomenon, known as flexoelectricity, affects the functional properties of insulators, particularly thin films of high permittivity materials. We have measured strain-gradient-induced polarization in single crystals of paraelectric SrTiO$_3$ as a function of temperature and orientation down to and below the 105 K phase transition. Estimates were obtained for all the components of the flexoelectric tensor, and calculations based on these indicate that local polarization around defects in SrTiO$_3$ may exceed the largest ferroelectric polarizations. A sign reversal of the flexoelectric response detected below the phase transition suggests that the ferroelastic domain walls of SrTiO$_3$ may be polar.