Intergranular Stress Induced Phase Transition in CaZrO ₃ Modified KNN‐Based Lead‐Free Piezoelectrics

The phase transition temperatures of CaZrO 3 ‐doped (Na 0.49 K 0.49 Li 0.02 )(Nb 0.8 Ta 0.2 )O 3 lead‐free piezoelectrics ( LKNNT ‐ CZ 5) have been studied with X‐ray diffraction and Raman scattering. It is found that LKNNT ‐ CZ 5 ceramics and powders with the same crystallite size (~2–5 μm) exhibit distinctly different phase transition behaviors versus temperature. The ceramic bulk changes its orthorhombic phase to tetragonal structure abruptly after being pulverized to powders at room temperature( RT ), and follows a phase transition sequence with increasing temperature: orthorhombic ( RT –65°C), orthorhombic and tetragonal (65°C–105°C), and tetragonal phase (105°C to ~220°C). Contrastively, the powders hold a tetragonal structure without any phase transition within the whole temperature region ( RT –220°C). These differences might be induced by the existing internal stress or residual strain, which could be released during the grinding process.