Lead-free piezoelectric ceramics - Properties and applications

Piezoelectric ceramics of the lead zircono-titanate type, with the general formula PbZr _1-x T _ix O ₃ (PZT), discovered in the 1950s, have been intensively studied and are massively used in many industrial applications (transducers, sensors, ultrasonic motors) due to their high-performance electromechanical properties. However, the development of electrical and electronic equipment has been marked by a growing awareness of the health and environmental impacts of the materials used. Legislation was progressively introduced, first in Japan, then in Europe, China and the United States, with the aim of limiting the use of toxic substances. Among the elements targeted is lead, whose toxicity is no longer in doubt. This situation led several laboratories around the world to carry out in-depth studies in search of new lead-free compositions with a perovskite structure and dielectric and piezoelectric properties comparable to those of PZT. As a result of the studies, three major families of lead-free piezoelectric materials were developed: BaTiO ₃ , K _x Na _1-x NbO ₃ and Bi _x Na _1-x TiO ₃ /BiFeO ₃ .

This article is divided into two main sections. After a review of the specific properties of piezoelectric materials, particularly PZTs, we focus on the environmental context and the benefits of obtaining lead-free piezoelectric materials. In the second part, we list the three main families of piezoelectric materials, their synthesis routes, the optimization of their properties through chemical composition modification, and their potential applications.