Review of Sintering Aids in Lead-Free (K, Na)NbO₃-Based Ceramics

With the conventional solid-state reaction method, it is generally difficult to fabricate dense (K, Na)NbO3 (KNN)-based ceramics because of the volatilization of alkali metal ions under high processing temperature. The addition of sintering aids is an effective way to improve the compactness of KNN-based ceramics in that they can suppress the volatilization of these ions by reducing the sintering temperature. Many efforts have been made to improve the sinterability of KNN-based ceramics and realize a dense microstructure, and the well-sintered KNN-based ceramics were obtained under relatively low sintering temperature. In this mini-tutorial, the mechanism of action of the sintering aids is discussed, and the effects of various sintering aids on the sintering characteristics of KNN-based ceramics are also emphasized. In addition, we also review the influence of the sintering aids on microstructure and electrical properties. Finally, we summarize the article and offer the prospect. This article will provide the reference for the selection of sintering aids in KNN-based ceramics.