Enhanced flexoelectric response of BaHf<i>x</i>Ti1−<i>x</i>O3 ceramics through polymorph phase boundary in spontaneously polarized surface

Abstract

Ferroelectric ceramics typically exhibit ultrahigh flexoelectric coefficients that far exceed theoretical values due to various extrinsic factors. It has been demonstrated that the high values are mostly contributed by the surface piezoelectric response of spontaneously polarized surface layers, and their proportion even exceeds 99%. Herein, we introduced polymorph phase boundary (PPB) into the polarized surface layers of BaHf0.01Ti0.99O3 ceramics in order to enhance the surface piezoelectric response. Ultimately, an ultrahigh effective flexoelectric coefficient (μρ) of ∼ 550 μC/m was obtained in the BaHf0.01Ti0.99O3 ceramics at room temperature, the maximum μρ reaching 910 μC/m at the Curie temperature (TC), which is more than that of other BaHfxTi1−xO3 ceramics. The large surface piezoelectric response of BaHf0.01Ti0.99O3 ceramics can persist up to TC, which should be attributed to the biaxial stress clamping PPB in the polarized surface layers, allowing the high μρ to be maintained close to the TC. Our study not only provides a strategy to enhance the flexoelectric coefficients in ferroelectric ceramics but also aids in a deeper understanding of the significant contribution of the polarized surface layers to the flexoelectric coefficients.