Study on the sintering mechanism of KNN-based lead-free piezoelectric ceramics

The sintering process and mechanism of (K, Na, Li) (Nb, Ta, Sb)O₃ (KNLNTS) solid solution were investigated. The results show that the KNLNTS forms via the reaction of A₂CO₃(A: K,Na,Li) and B₂O₅(B: Nb,Ta,Sb) at 400–800 °C. The kinetics for the formation of KNLNTS during solid-state reaction is investigated using an isothermal method. Based on the reaction kinetic isothermal analysis, KNLNTS formation is corroborated as being controlled by diffusion mechanism. It has been found that sintering densification occurs within a narrow temperature range, and the density decreases apparently when the sintering temperature slightly exceeds the optimal one. Abnormal grain growth tends to occur after reaching the maximum density and get intensified with increasing temperature. The effect of sintering temperature and time on the shrinkage of powder compacts during sintering were studied. The sintering process in the KNLNTS solid solutions may be explained by the grain boundary diffusion model inferring from the shrinkage rate of about 0.3.