High remnant polarization of (K0.5Na0.5)0.99(Ba0.0025Sr0.0025)NbO3 piezoceramics with nano-CuO sintering aid

In this study, pure KNN and Ba/Sr co-doped KNN with and without nano-CuO (nCuO) as sintering aid (0.5 mol%) were prepared by the solid-state method. The results showed that both Ba/Sr co-doping and nCuO sintering aid efficiently improved the densification process, piezoelectric and dielectric properties of the KNN ceramic. The Ba/Sr co-doped KNN samples with nCuO showed a high piezoelectric coefficient (d(33) = 176 pC/N), a high dielectric constant (epsilon(r) = 623), a low dielectric loss (tan delta = 0.009) and a high remnant polarization (33 mu C/cm(2)). The Ba/Sr dopants and nCuO sintering aid could transform the tetragonal phase to orthorhombic ones for KNN ceramics and by the substitution of Cu2+ at the B-site of the perovskite structure formed the oxygen vacancies that could improve the densification. Furthermore, it was found out that the density has a significant effect on the electrical properties of sintered samples. With increase in the relative density, the d(33), and epsilon(r) of KNN ceramics expansively increased, and the tan delta of the samples linearly decreased.