Lead-free KNN-based piezoelectric materials

Lead-free piezoelectric materials have recently been given vast attention due to environmental issues and the toxicity of their lead-based counterparts. One of the potential lead-free candidates is the xKNbO₃-(1-x)NaNbO₃ binary system. The K_0.5N_0.5NbO₃ composition in particular exhibits relatively high Curie temperature and the highest electromechaical and ferroelectric response among the possible K _x Na_1-x NbO₃ compositions. The present chapter covers some fundamental issues regarding the crystal chemistry, material processing, and dielectric and ferroelectric behavior of KNN-based piezoelectrics. The topics discussed in this context fall into four categories: KNN-based polycrystalline ceramics, textured ceramics, single crystals, and thin films. The recent research activities concerning the most promising compositions, processing techniques, and some of the challenges encountered in obtaining high performance Pb-free piezoelectric materials have been reviewed for each category.