Ferroelectricity temperature characterizes of hardened KNN–CC lead-free piezoceramics

The qualitative and quantitative analyses of ferroelectricity temperature characterizes for (K_0.48Na_0.52)NbO₃–1 mol%CuO–1 mol%Co₂O₃ (KNN–CC) lead-free piezoceramic has been systematically investigated. KNN–CC ceramic shows an asymmetric P–E loops at various temperatures, and remnant polarization (P_r) reaches the maximum at T ~ 80 °C. Dynamic hysteresis characterizes indicate orthorhombic (O) to monoclinic (M) phase transition occurs round 80 °C. Large internal bias electric field (E_i) is attributed to defect dipoles polarization (P_D), which is difficult to orientation because of low migration rate of defects. Moreover, owing to CuO and Co₂O₃ additives, the space charge cluster at grain boundary confirmed by impedance spectroscopy (IS) analysis result in enlarged E_i with increasing temperature. Mechanical quality factor (Q_m ~ 868) of aged KNN–CC ceramic is almost doubled that of unaged one. In short, both defects and phase structure affect the temperature stability of ferroelectricity and macroscopic electrical property for KNN lead-free piezoceramics.