Flexoelectric-boosted piezoelectricity of BaTiO3@SrTiO3 core-shell nanostructure determined by multiscale simulations for flexible energy harvesters

Achieving lead-free piezoelectric nanoparticles with excellent electromechanical responses is in great demand for fabricating nanoscale electronic devices. Recently, the coupling effect of combining flexoelectricity and piezoelectricity has attracted attention as a promising approach to control electromechanical properties. However, the implication of the coupling for the nanoparticles in this regard has been challenging due to its difficulty in controlling and observing the internal strain gradient. In this study, we demonstrate the flexoelectric-boosted electromechanical properties of piezoelectric nanoparticles using an induced built-in strain gradient in heterogeneous core-shell nanostructure. The composition-graded core-shell structure of BaTiO3@SrTiO3 nanoparticles enables a significant increment of the effective piezoelectric charge coefficient via the chemical heterogeneities-induced lattice strain gradient. Through the combinations of ab-initio calculation and multiphysics simulations, the origin of the strain distribution over nanoparticles is theoretically interpreted with accompanying phase balance and diffusion criteria. In addition, our designed core-shell nanoparticles-based energy harvesting devices generate highly efficient and flexoelectric-boosted piezoelectric output signals. Individual core-shell nanoparticles and related elastomeric nanocomposites reported in this work represent state-of-the-art electromechanical properties compared to previously reported piezoelectric nanoparticles and composites. This study provides a new source of inspiration for achieving high-performance lead-free piezoelectric nanostructures, paving the way for developing nano-electromechanical applications.