Low-temperature sintering and piezoelectric properties of 0.65Pb(Zr _1-xTi_x)O₃-0.35Pb(Ni_0.33Nb _0.67)O₃ ceramics

0.65Pb(Zr_1-xTi_x)O₃-0.35Pb(Ni _0.33Nb_0.67)O₃ (0.65PZTx-0.35PNN) ceramics exhibited a morphotropic phase boundary at approximately x=0.58-0.59. The 0.65PZT58-0.35PNN ceramics sintered at 1200°C exhibited the high piezoelectric properties of d₃₃=605pC/N, k_p=0.61, and ε₃^T/ε₀=3600. The sintering temperature of the PZT58-PNN ceramics decreased from 1200 to 850°C with the addition of a small amount of CuO. The CuO reacted with the PbO and formed a liquid phase during sintering, which assisted in the densification of the specimens. Most of the Cu²⁺ ions existed in the CuO second phase, thereby preventing any possible hardening effect due to the Cu²⁺ ions. The Curie temperature of the 0.65PZT58-0.35PNN ceramic was approximately 200°C and was not altered by the addition of CuO. The d₃₃, k _p, and ε₃^T/ε₀ values of the 0.65PZT58-0.35PNN ceramics were considerably increased with the addition of CuO and similar results were also observed for the 0.65PZT59-0.35PNN ceramics. In particular, 1.0 mol% CuO-added 0.65PZT58-0.35PNN ceramics sintered at 900°C exhibited the high piezoelectric properties of d₃₃=620 pC/N, k_p=0.64, and ε₃^T/ε₀= 3750. Moreover, the reaction between the Ag electrode and the Cu-added 0.65PZT58-0.35PNN ceramic sintered at 900°C was negligible.