Giant flexoelectric coefficients at critical ferroelectric transition

Flexoelectric materials, which could generate polarization in response to a strain gradient, could be utilized in a wide range of devices such as actuators and sensors. However, the flexoelectric coefficients of most dielectrics are too small to be utilized. One of the most promising flexoelectric materials is ferroelectrics whose flexoelectric coefficients are orders of magnitude higher than those of ordinary dielectrics. Despite of intensive research in the past twenty years, the record-high flexoelectric coefficient (μ1122=100μC/m) of Ba0.67Sr0.33TiO3 ferroelectric has not been surpassed. Here we show that by tuning the first-order paraelectric-ferroelectric phase transition of BaTiO3 to near-critical through doping BaZrO3, a drastic enhancement of flexoelectric coefficient (μ1122=140μC/m) occurs, which is ascribed to the enhancement of both intrinsic and extrinsic flexoelectricity resulting from the strong lattice instability at the critical transition. This study demonstrates a general design method to achieve high flexoelectric coefficients in a wide range of ferroelectric systems through searching for critical ferroelectric transition points.