In our everyday life, we use devices that transform electrical energy into mechanical energy and vice-versa. This energy conversion happens in sensors, actuators and energy-harvesters used in consumer electronics, medical diagnosis, and self-powered devices, to name a few. Most of these devices rely nowadays on piezoelectric materials, which nevertheless are brittle, expensive, and non-biocompatible. Furthermore, the best and most widely used piezoelectrics have high contents of toxic lead. For these reasons, there is a need to develop new materials for electro-mechanical transduction. Beyond the chemical synthesis of new piezoelectric materials, this project explores the use of another electromechanical coupling, flexoelectricity, which is universal in dielectrics and thus naturally allows for electromechanical transduction in a much wider range of materials. Flexoelectricity is the coupling between electric polarization and strain gradient, and conversely between strain and polarization gradient, i.e. it requires inhomogeneous deformation. It is significant at small scales, where high-gradients develop. It has been suggested that flexoelectricity could enable piezoelectric metamaterials made out of non-piezoelectric components, including soft materials. This would significantly broaden the class of materials used for electro-mechanical transduction, which could enable affordable, environmentally-friendly, biocompatible and self-powered small-scale devices. However, our understanding of the fundamental origin of flexoelectricity or of how to exploit it in practice is very poor. The objective of this project is to develop an advanced computational infrastructure to quantify flexoelectricity in solids, focusing on continuum models but also exploring multiscale aspects, in tight collaboration with experiment. We have explored the effects of strain and polarization gradients on the physics of dielectrics, identifying fundamental manifestations and extracting the underlying engineering principles for a new generation of electromechanical metamaterials.
