Room temperature surface piezoelectricity in SrTiO3 ceramics via   piezoresponse force microscopy
  SrTiO3 ceramics are investigated by piezoresponse force microscopy. Piezoelectric contrast is observed on polished surfaces in both vertical and lateral regimes and depends on the grain orientation varying in both sign (polarization direction) and amplitude. The observed contrast is attested to the surface piezoelectricity due to flexoelectric effect (strain gradient-induced polarization) caused by the surface relaxation. The estimated flexoelectric coefficient is approximately one order of magnitude smaller as compared to those recently measured in SrTiO3 single crystals. The observed enhancement of piezoresponse signal at the grain boundaries is explained by the dipole moments associated with inhomogeneous distribution of oxygen vacancies. 
Andrei Kholkin, Igor Bdikin, Tetyana Ostapchuk, and Jan Petzelt