High-performance KNN piezoceramics with reproducibility and chemical stability. Part I: Solid-state reaction route

(K,Na)NbO3-based compounds are attracting much attention for their high potential as Pb-free piezoelectric ceramics. They have, however, three major drawbacks to overcome in order to achieve a mature development: densification, reproducibility, and chemical stability. In this first part, based on standard solid-state reaction, the way to synthesize high-density homogeneous ceramics with high piezoelectric performance and chemical stability is elucidated. It relies on a low-temperature spark-plasma sintering process, after the raw materials have been finely pulverized prior to reaction. The reproducibility, however, remains a pending issue due to the unavoidable random formation of parasitic phases.