Potassium-sodium-niobate-based thin films: Lead free for micro-piezoelectrics

Extensive research and great progress of (K,Na)NbO${}_3$ (KNN)-based lead-free piezoelectric films have been driven by the current legislation and the requirement for sustainable development of society and environment in the applications of microelectromechanical systems. A comprehensive discussion of the recent achievement in KNN-based films is presented herein. First, the available synthetic techniques, chemical modification, the ferroelectric and piezoelectric properties of KNN-based films are reviewed, followed by an introduction of the crystal structures and electrical properties of KNN-based epitaxial films in comparison with the bulk ceramics. Finally, the applications of KNN-based films for the sensors, the energy harvesters, and energy storage devices are addressed, and current challenges and prospects for future work are discussed. (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)