Effects of modified-process on the microstructure, internal bias field, and activation energy in CuO-doped NKN ceramics

In this study, (Na0.5K0.5)NbO3 + xCuO (NKNCx, where x = 0–1 mol%) were separately prepared using the two-step calcination process (BO method) and a conventional mixed oxide method (MO method). The microstructure of NKNCx ceramics prepared using the MO method exhibited obviously inhomogeneous microstructure. In contrast, the BO method improved the compositional homogeneity as well as the electrical properties. A high Qm value of 2100 was obtained for NKNCx ceramics prepared using the BO method. The ceramics prepared using the BO method exhibited the formation of more oxygen vacancies, resulting in an increase in the internal bias field. The value for the activation energy of the samples supports the presence of oxygen vacancies. The bulk density, dielectric loss, kp, Qm, d33 and ɛ33T/ɛ0 of the NKNCx ceramics prepared using the BO method were 4.488 g/cm3, 0.15%, 41.5%, 2100, 95 pC/N and 280, respectively.