Mechanistic interpretation of the reactive templated grain growth process of (Li, Ta, Sb) modified (K, Na)NbO3 textured lead-free piezoceramics

Abstract

Reactive templated grain growth (RTGG) is a promising synthetic method for textured ceramics especially for high performance lead-free piezoceramics. However, the sintering mechanism in a RTGG process remains unclear. In this study, we perform detailed structural and compositional characterization of KNN-based piezoceramics sintered at four elevated temperatures, i.e. 800 °C, 1100 °C, 1140 °C and 1190 °C, in order to precisely examine the phase and microstructure evolution during the RTGG processes. Upon increasing the temperature up to 1190 °C, the sintering system undergoes successive processes, including elemental interdiffusion between the matrix grains and NN templates, formation of a eutectic compound and hence melting of matrix grains, nucleation and epitaxial growth on template surfaces, and finally coarsening of epitaxial crystals by consuming the intermediate liquid phase. Finally, suggestions for rational design and fabrication of textured lead-free piezoceramics using RTGG are proposed.