Differences between copper-oxide- and zinc-oxide-doped sodium potassium niobate ceramics

(Na _0.5K _0.5)NbO ₃is doping with ZnO and CuO, respectively, (NKNZx and NKNCx, where x = 0-1 mol%) using a two-step calcination process (BO method). The X-ray diffraction profiles of NKNZx ceramics show a few secondary phases because Zn ²⁺ ions cannot substitute Nb ⁵⁺ ions. Moreover, the binding energies of Nb atoms in CuO- and ZnO-doped NKN ceramics are different, suggesting that oxygen vacancies were induced when CuO was doped into NKN ceramics. The mechanical quality factor (Q _m) values of the NKNZx ceramics are not as high as those of NKNCx ceramics due to a lack of oxygen vacancies in the former. The internal bias field is used to demonstrate the presence of oxygen vacancies. In ZnO-doped NKN ceramics, the piezoelectric properties only improved slightly because ZnO used as a sintering aid enhanced the densification of samples. A high Q _mvalue is obtained for CuO-doped NKN ceramics mainly due to the formation of oxygen vacancies.