Advances in development of Pb-free piezoelectric materials for transducer applications

Pb-based ferroelectrics and piezoelectrics in the form of bulk polycrystalline and textured ceramics, single crystals, and composites, have been used in sensors, actuators, and other electromechanical devices. However, the toxicity of these materials has been a major concern around the globe for the past few decades. The report of high piezoelectric activity in the lead-free BaTiO3 (BT), (Bi0.5Na0.5)TiO3 (BNT), and (K-0.5,Na-0.5)NbO3 (KNN) and binary and ternary systems with other compounds has given high hopes for alternatives to Pb-based materials. Recent modifications of KNN-based compositions with BaZrO3 in combination with (Bi-0.5,K-0.5)HfO3 result in excellent electromechanical properties. Therefore, increased research and development in Pb-free materials brings hope for practical applications closer to reality. In this article, the recent developments on BT, BNT, and KNN reproducible soft and hard Pb-free piezoelectric compositions with a range of electromechanical properties for low- and high-power transducer applications will be reviewed. Several examples in the development of lead-free HF ultrasound transducers will be presented.