Structural origin of excellent fatigue resistance in KNN-based ceramics with multiphase coexistence

Abstract

By constructing polymorphic multiphase coexistence, excellent piezoelectric properties and fatigue resistance have been obtained in potassium sodium niobate (KNN)-based ceramics, which was considered with great potential to replace lead-based ceramics. However, the potential structural origin and physical mechanism for the improvement of fatigue resistance are worth further exploration. Here, two kinds of KNN ceramics with orthorhombic phase and rhombohedral-orthorhombic-tetragonal mixed-phase were designed to investigate the fatigue behavior as well as the behind contributing factors. Excellent fatigue resistance under cyclic electric field was found in ceramic with multi-phase coexistence, but the ceramic with orthorhombic phase shows obvious electrical fatigue. Through analyzing the macro-meso-micro structure before and after fatigue, the multiphase coexistence state, stable microstructure and easily rotated miniaturized domains synergistic contributed to the enhancement of fatigue stability. On the contrary, the performance degradation of orthorhombic one is due to the blocked and pinned large size domains during the fatigue process as well as the microstructure damage.