Structural electroactive cermets: dielectric and structural properties of conductive metallic reinforced piezoelectric ceramics

More efficient transportation, structural energy storage systems, active sensing, and self-diagnosis are examples where disruptive materials are necessary for driving technological innovation forwards. Unprecedented combinations of properties can be achieved when materials of dissimilar nature and contrasting properties like metals and ceramics are merged. For multimaterial systems, the key challenge is to develop suitable manufacturing processes as to be able to, first, successfully produce the material and, second, to achieve the desired behavior without compromising the integrity of the combined materials. A particular interesting class of material is what are defined in this work as structural electroactive cermets: composite materials constituted by conductive ductile metallic particles dispersed within and used as reinforcement for an insulating dielectric matrix. Specifically, chemically unreactive conductive second-phase reinforcing metallic particles such as Ag or Pt are added to piezoelectric ceramics aiming to enhance their brittle mechanical behavior. As analyzed in the present review, the quest for better mechanical properties results in the enhancement of the dielectric properties in general and of the dielectric constant in particular via the percolation effect for which the percolation theory and other alternative models are discussed. Finally, challenges are identified and potential areas of scientific interest for further developments proposed.