Effect of Post-Annealing on the Microstructure and Microwave Dielectric Properties of Ba(Co0.7Zn0.3)1/3Nb2/3O3 Ceramics

The effects of post-annealing on the crystal structure, microstructure, and microwave dielectric properties for Ba(Co0.7Zn0.3)1/3Nb2/3O3 ceramics were investigated. The as-prepared materials were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The microwave dielectric properties are measured at 6 GHz using a network analyzer. Ba5Nb4O15 and/or Ba8(Co,Zn)1Nb6O24 secondary phases were found on the surface according to sintering conditions due to volatilization of some Zn and Co elements. The experimental results show that the beneficial effect of the annealing steps to improved the microwave dielectric properties. Excellent microwave dielectric properties were achieved for the coarse-grained microstructures by a higher sintering temperature and with a shorter holding time followed by annealing steps at lower temperatures with a longer holding time. This improvement can be attributed to 1:2 cation ordering within the crystal, which is taking place during annealing process. The Ba(Co0.7Zn0.3)1/3Nb2/3O3 ceramic could be used successfully for realization of dielectric microwave resonators, since it has a high quality factor Qf value of 123,700 GHz, a high dielectric constant εr value of 34.5 and a temperature coefficient of the resonant frequency τf of 0 ppm/°C.