Structure and asymmetric ferroelectric loops of (K0.48Na0.52)NbO3-1mol%CuO-xmol%Co2O3 ceramics with low-temperature sintering

Lead-free piezoelectric ceramics, (K0.48Na0.52)NbO3-1 mol%CuO-x mol%Co2O3 [KNN-Cu-xCo hereafter], were prepared by a conventional solid-state sintering method, and the low-temperature sintering behavior and ferroelectric property of Co2O3 doped (K0.48Na0.52)NbO3 piezoelectric ceramics were investigated. It was found that CuO and Co2O3 additions are very effective to improve the density and sintering behavior of KNN ceramics. KNN-Cu-0.1Co ceramics with the highest density (ρ ∼ 4.38 g/cm3) could be prepared at such a low sintering temperature of 930 °C. Hard ferroelectrics KNN-Cu-xCo show an asymmetric P-E hysteresis loop, attributing to an internal bias field Ei. The improvement measures of Ei was discussed through the analysis on its affected factors, including doped level, sintering temperature, and measuring frequency. The results also suggested that mechanical quality factor Qm has similar variation trend with Ei as the variation sintering temperature or composition. KNN-Cu-0.5Co ceramics sintered at 980 °C obtain the excellent properties: Qm ∼ 577, kp ∼ 30% and d33 ∼ 83 pC/N.