Field-induced piezoelectricity in SrTiO3 at room temperature determined by interferometric measurement

Abstract

Defect engineering is an effective tool to manipulate material properties and produce completely new ones that are symmetry-forbidden in a defect-free crystal. For example, single crystals of SrTiO3 form, as a long-term reaction to external static electric fields, a strained near-surface layer through the migration of oxygen vacancies out of the area beneath the positively charged electrode. It was previously shown that this near-surface phase exhibits pyroelectric and piezoelectric properties, which are symmetry-forbidden in centrosymmetric bulk SrTiO3. In the present paper, different approaches have been used to better understand the nature of this reaction. In situ XRD measurements were carried out to investigate the dynamics of the lattice distortion during the formation and relaxation of this phase. Interferometry measurements were carried out to determine the piezoelectric thickness change of the samples and to indirectly investigate the polar property of the unit cell before, during, and after electroformation. We observe the instantaneous formation of a polar strontium titanate unit cell at room temperature, explainable by electrostriction, and the expected additional contribution after a long-term field application.