Flexoelectricity in compositionally graded Ba1-xSrxTiO3 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 Ba1-xSrxTiO3 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 degrees C in single component ceramics (such as Ba0.67Sr0.33TiO3 and BaTiO3) can be significantly reduced in graded Ba1-xSrxTiO3 ceramics, in which the flexoelectric coefficient is in the range from 13 to 26 mu C/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.