Contribution of polar nanorregions to the giant flexoelectricity of relaxor ferroelectrics

We have studied the bending-induced polarization of single crystal relaxor ferroelectrics close to a morphotropic phase boundary. Anomalously large flexoelectric and flexocoupling coefficients were registered, with values well in excess (up to 10 times bigger) than theoretical expectations based on Kogan's theory [1] below critical temperature. The temperature dependence of the effective flexoelectric coefficients shows that this anomalous enhancement persists in the temperatures up to T* $\sim$ 250$^{\circ}$C, above which the values fall back in line with theoretical expectation for pure flexoelectricity. Cross-correlation between flexoelectric and elastic measurements indicates that the anomalous enhancement of bending-induced polarization is caused by the flexoelectric reorientation of non-percollating polar nanotwins that exist in the temperature range between Tc and T*. \\[4pt] [1] S. M. Kogan, Soviet Physics Solid State, 5, (1964) 2069.