  Flexoelectricity has garnered much attention owing to its ability to bring
electromechanical functionality to non-piezoelectric 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 characterize the flexoelectric response of bulk centrosymmetric
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 ~4x
at elevated temperatures. Additionally, we observe time-dependent and
non-linear 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.
