Advanced Lead-Free Piezoelectric Materials: Ceramics, Polymers, and Composites

Piezoelectric materials have the intrinsic capability of transducing mechanical stimuli into electrical signals (voltage, current), and they can be synthesized in plenty of diverse forms (thin films, nanosheets, nanoparticles, nanopillars, multilayer structures, nanofibers, etc.). Hence, they are very attractive for several applications: nanoenergy generation, sensing, actuation, and biomedical implants. The highest performances of charge generation, usually expressed in terms of piezoelectric coefficients, are found in lead-based materials, such as lead zirconate titanate (PZT) and its family. These materials are really effective, but they are environmentally unfriendly and toxic. Therefore, lead-free alternatives to PZT-based piezoelectrics have become urgently necessary, and some novel examples have been explored throughout the years, such as barium titanate or lithium niobate (BaTiO3, LiNbO3) families, aluminum nitride (AlN), zinc oxide (ZnO), etc. Besides piezo-ceramic materials, many polymers can exhibit a piezoelectric behavior. Even though their performances are lower, their flexibility, biocompatibility, and ease of processing make them preferable for certain applications. The most common example is poly(vinylidene fluoride), PVDF, and its copolymers, but other piezo-polymers have been discovered and analyzed in the recent years (e.g., PLLA, parylene, chitin, cellulose, chitosan, etc.). This chapter describes the current research status and advances in lead-free piezoelectric materials, highlighting their properties and applications.