Enhanced flexoelectric properties in sodium bismuth titanate-based lead-free relaxor ferroelectrics by inducing polar nanoregions

Abstract

The presence of polar nanoregions (PNRs) is widely recognized as playing a crucial role in the functionalities of numerous solid dielectrics. However, the contribution of PNRs to the specific coupling between strain gradient and electric polarization (flexoelectricity) has not yet been thoroughly understood. Herein, we investigated the impact of varying PNR concentrations on the dielectric and flexoelectric properties of lead-free relaxor ferroelectric (Bi0.5Na0.5)TiO3 ceramics, achieved through stoichiometric BaTiO3 doping. The temperature-dependent dielectric properties indicated the presence of PNRs in doubly doped ceramics as compared to pure BNT. Complex impedance analysis and piezoresponse force microscopy measurements demonstrated significant differences in PNR concentrations among the different components. The reorientation of PNRs notably enhanced the flexoelectric response of the doubly doped BNT-xBT ceramics, with this enhancement being positively correlated with the concentration of PNR. Specifically, the flexoelectric coefficient was found to be approximately 10 times higher in the morphotropic phase boundary (MPB) region (x = 0.08) compared to pure BNT. These findings illustrate that adjusting the concentration of PNRs in lead-free relaxation ferroelectrics is an effective strategy for improving flexoelectric properties.