Flexoelectricity in compositionally graded Ba_1−xSr_xTiO₃ ceramics

Flexoelectricity, the coupling between electric polarization and strain gradients in dielectrics, attracts growing research interest because of its potential to replace/complement piezoelectricity in electromechanical applications. Thanks to the large dielectric permittivity, ferroelectrics exhibit enhanced flexoelectricity and usually serve as the functional ingredient in flexoelectric devices. However, ferroelectric flexoelectricity usually suffers from poor temperature stability, which adversely affects practical applications. In this work, compositional gradients are introduced into Ba_1−xSr_xTiO₃ systems to enhance the temperature stability of flexoelectric behavior. Experimental results show that the drastic variations of flexoelectricity (up to 100 times) from 20 to 120 °C in single component ceramics (such as Ba_0.67Sr_0.33TiO₃ and BaTiO₃) can be significantly reduced in graded Ba_1−xSr_xTiO₃ ceramics, in which the flexoelectric coefficient is in the range from 13 to 26 μC/m. The improved stability results from the engineered sequential Curie temperatures of individual layers in graded ceramics and the positive correlation between dielectric constant and flexoelectricity. Our work provides a method to enable the robust performance of flexoelectric devices in an ambient environment with large temperature fluctuations.