Effects of ZnO/Li₂O codoping on microstructure and piezoelectric properties of low-temperature sintered PMN-PNN-PZT ceramics

Pb(Mg_1/3Nb_2/3)O₃-Pb(Ni_1/3Nb_2/3)O₃-Pb(Zr_1/2Ti_1/2)O₃ (designated as PMNT) piezoelectric ceramics codoping with Zn²⁺/Li⁺ were prepared and the effects of ZnO/Li₂O (Z/L) additive on microstructure, piezoelectric and dielectric properties were investigated. The results show that the pure perovskite phase is formed and the phase structure changes from tetragonal to rhombohedral with different Z/L weight ratios. The Curie temperature T_c, dielectric constant ε, electromechanical coupling factor k_p and piezoelectric constant d₃₃ decrease, whereas mechanical quality factor Q_m increases with Z/L weight ratio changing from 1:1 to 1:8. The optimized Z/L weight ratio is 1:1. It is revealed that k_p and d₃₃ first increase then decrease, whereas Q_m changes opposite with increasing content of Z/L additive. The PMNT ceramic with Z/L ratio 1:1 and the amount of 1 wt% has excellent piezoelectric properties: k_p = 0.60, d₃₃ = 397 pC/N, T_c = 251 °C, Q_m = 150, ε = 2628 and tan δ = 0.0296, when sintered at 960 °C. Finally, multilayer piezoelectric actuator is prepared using optimal composition by tape casting. The actuator shows the displacement characteristics of 3.3 μm under electric field 100 V/mm.