The origins of electromechanical indentation size effect in ferroelectrics

Metals exhibit a size-dependent hardening when subject to indentation. Mechanisms for this phenomenon have been intensely researched in recent times. Does such a size effect also exist in the electromechanical behavior of ferroelectrics?-if yes, what are the operative mechanisms? Our experiments on BaTiO3 indeed suggest an elastic electromechanical size effect. We argue, through theoretical calculations and differential experiments on another nonferroelectric piezoelectric (quartz), that the phenomenon of flexoelectricity (as opposed to dislocation activity) is most likely responsible for our observations. Flexoelectricity is the coupling of strain gradients to polarization and exists in both ordinary and piezoelectric dielectrics. In particular, ferroelectrics exhibit an unusually large flexoelectric response. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3231442]