Direct Observation of Huge Flexoelectric Polarization around Crack Tips

Flexoelectricity is especially relevant for nanoscale structures, and it is expected to be largest at the tip of cracks. We demonstrate the presence of a huge flexoelectric polarization at crack tips in SrTiO₃ by direct observation with scanning transmission electron microscopy. We observe an averaged polarization of 62 ± 16 μC cm^-2 in the three unit cells adjacent to the crack tip, which is one of the largest flexoelectric polarizations ever reported. The polarization is screened by an electron density of 0.7 ± 0.1 e^-/uc localized within one unit cell. These findings reveal the relevance of flexoelectricity for the science of crack formation and propagation.