Influence of secondary phase on polymorphic phase transition in Li-doped KNN lead-free ceramics

Shifting polymorphic phase transition (PPT) to room temperatures in Li-doped KNN (KNLN) can greatly increase its piezoelectric constant. However, pure phase KNLN ceramics could hardly be obtained since secondary phases were formed inevitably during its synthesis. Here, we examined the structure, composition and distribution of the secondary phase and their influences on the phase compositions in KNLN ceramics. The results show that orthorhombic tetragonal phase boundary cannot shift to room temperature when considerable amount of secondary phase exist in KNLN piezoceramics.