Origin of the enhanced flexoelectricity of relaxor ferroelectrics

We have measured the bending-induced polarization of Pb(Mg1/3Nb2/3)O-3-PbTiO3 single crystals with compositions at the relaxor-ferroelectric phase boundary. The crystals display flexocoupling coefficients f> 100 V, an order of magnitude bigger than the theoretical upper limit set by the theories of Kogan and Tagantsev. This enhancement persists in the paraphase up to a temperature T*=500 +/- 25K that coincides with the onset of anelastic softening in the crystals; above T*, the true (lattice-based) flexocoupling coefficient is measured as integral(13) approximate to 10V for both compositions. Cross-correlation between flexoelectric, dielectric, and elastic properties indicates that the enhancement of bending-induced polarization of relaxor ferroelectrics is not caused by intrinsically giant flexoelectricity but by the reorientation of polar nanodomains that are ferroelastically active below T*. (C) 2014 AIP Publishing LLC.