Ferroelastic Twin-Wall-Mediated Ferroelectriclike Behavior and Bulk Photovoltaic Effect in SrTiO3

R He and HW Xu and PJ Yang and K Chang and H Wang and ZC Zhong, PHYSICAL REVIEW LETTERS, 132, 176801 (2024).

DOI: 10.1103/PhysRevLett.132.176801

Ferroelastic twin walls in nonpolar materials can give rise to a spontaneous polarization due to symmetry breaking. Nevertheless, the bistable polarity of twin walls and its reversal have not yet been demonstrated. Here, we report that the polarity of SrTiO 3 twin walls can be switched by an ultralow strain gradient. Using first -principles -based machine -learning potential, we demonstrate that the twin walls can be deterministically rotated and realigned in specific directions under the strain gradient, which breaks the inversion symmetry of a sequence of walls and leads to a macroscopic polarization. The system can maintain polarity even after the constraint is removed. As a result, the polarization of twin walls can exhibit a ferroelectriclike hysteresis loop upon cyclic bending, namely flexoferroelectricity. Finally, we propose a scheme to experimentally detect the polarity of the twin wall by measuring the bulk photovoltaic responses. Our findings suggest a twin -wall -mediated flexoferroelectricity in SrTiO 3 , which could be potentially exploited as functional elements in nanoelectronic devices design.

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