Large Thermal–Electrical Response and Rectifying Conduction Behavior in Asymmetrically Reduced Ferroelectric Ceramics

The thermal energy is normally converted into electrical power by the thermoelectric effect or pyroelectricity of materials, and a variation of temperature with time or space is required during the conversion. Here, we demonstrate that the thermal–electrical conversion can be realized in a uniform temperature environment by exploiting the flexoelectric effect of ferroelectrics. After a chemical inhomogeneity is introduced to Na0.5Bi0.5TiO3-based ferroelectric ceramics via an asymmetrical reduction, the ceramics can function as thermal energy harvesters with a large power density of 0.18 mW/cm3. The large thermal–electrical response is attributed to the coupling of a significantly enhanced flexoelectric response, which causes a built-in electric field in the materials and increased conductivity after the reduction. The reduction-induced built-in field has a significant effect on the electrical conduction, and the reduced ceramics exhibit a rectifying conduction behavior even at a high temperature of 350 °C.