Enhanced flexoelectric-like response in oxide semiconductors

Flexoelectricity is a property of all dielectric materials whereby they polarize in response to deformation gradients such as those produced by bending. Although it is generally thought of as a property of dielectric insulators, insulation is not a formal requirement: in principle, semiconductors can also redistribute their free charge in response to strain gradients. Here we show that bending a semiconductor not only generates a flexoelectric-like response, but that this response can in fact be much larger than in insulators. By doping single crystals of wide-bandgap oxides to increase their conductivity, their effective flexoelectric coefficient was increased by orders of magnitude. This large response can be explained by a barrier-layer mechanism that remains important even at the macroscale, where conventional (insulator) flexoelectricity otherwise tends to be small. Our results open up the possibility of using semiconductors as active ingredients in electromechanical transducer applications.This research was funded by an ERC Starting grant from the EU (ERC 308023) and by a national research grant (FIS2013-48668-C2-1-P) from the Spanish MINECO. All research in ICN2 is supported by the Severo Ochoa Excellence Programme (SEV-2013-0295). F.V.-S. thanks MICITT and CONICIT for support during his PhD.Peer Reviewe