High‐performance KNN piezoceramics with reproducibility and chemical stability. Part II: Innovative melt‐reaction route

Abstract

AbstractIn the first part, a means to synthesize high‐density homogeneous (K,Na)NbO3 (KNN) ceramics with high piezoelectric performance and chemical stability at low spark‐plasma sintering temperature was found. However, these properties could not be obtained reproducibly, thus this second part is focused on solving this issue. Here, instead of doing a fine pulverization of raw materials prior to the reaction, the powders are ultimately mixed in the molten state and quenched to keep a single stoichiometry. A fast quenching is found to promote a better homogenization of the KNN phase upon annealing. Additionally, the coarse‐ground KNN powder is pre‐annealed before fine pulverization to preserve its high crystallinity. This innovative procedure prevents the formation of parasitic phases, leading with it to high‐performance undoped KNN ceramics (d33 ≈ 145 – 154 pC/N, kp ≈ 47–48% and kt ≈ 35 – 42%), while achieving both high reproducibility and chemical stability.