Twin-boundary-mediated flexoelectricity in LaAlO3

Flexoelectricity has garnered much attention owing to its ability to bring electromechanical functionality to nonpiezoelectric materials and its nanoscale significance. In order to move towards a more complete understanding of this phenomenon and improve the efficacy of flexoelectric-based devices, it is necessary to quantify microstructural contributions to flexoelectricity. Here we directly measure the flexoelectric response of bulk centrosymmetric ${\mathrm{LaAlO}}_{3}$ crystals with different twin-boundary microstructures. We show that twin-boundary flexoelectric contributions are comparable to intrinsic contributions at room temperature and enhance the flexoelectric response by $\ensuremath{\sim}4\ifmmode\times\else\texttimes\fi{}$ at elevated temperatures. Additionally, we observe time-dependent and nonlinear flexoelectric responses associated with strain-gradient-induced twin-boundary polarization. These results are explained by considering the interplay between twin-boundary orientation, beam-bending strain fields, and pinning site interactions, and directly demonstrate that macroscopic flexoelectric responses are very sensitive to structural defects.