(K, Na)NbO₃-based lead-free piezoceramics: Phase transition, sintering and property enhancement

Most widely used piezoelectric ceramics are based on Pb(Zr,Ti)O₃ (PZT) composition which has adverse environmental and health effects due to its high lead content. Environmental and safety concerns with respect to the utilization, recycling, and disposal of lead-based piezoelectric ceramics have induced a new surge in developing lead-free piezoelectric ceramics. Among all the lead-free ceramics, (K,Na)NbO₃ (KNN) has drawn increasing attention because of its well-balanced piezoelectric properties and better environmental compatibility. On basis of the author's work, this review summarizes the progress that has been made in recent years on development of KNN-based piezoelectric ceramics, including crystallographic structure and phase transition analysis, pressurized solid-state sintering as well as liquid-phase-assisted sintering process, and poling treatment for property enhancement. All in all, KNN is a promising lead-free system, but more research is still required both from academic and industrial interests.