Structure, Dielectric Properties, and Grain Growth Kinetics of MO-ZrO2-Ta2O5 (M = Zn, Co) Microwave Ceramics

MO-ZrO 2 -Ta 2 O 5 (M = Zn, Co) ceramics were prepared by solid-phase reaction method. Thermo-gravimetric-differential thermal behavior, crystal structure, and microwave dielectric properties of ZnO-ZrO 2 -Ta 2 O 5 and CoO-ZrO 2 -Ta 2 O 5 ceramics were compared in this paper. Both of them exhibited monoclinic wolframite structure. Densest microstructures with uniform grains were obtained at 1400°C and 1425°C in the cases of M = Zn and Co, respectively. ZnO-ZrO 2 -Ta 2 O 5 and CoO-ZrO 2 -Ta 2 O 5 exhibited comparable ε r  ~ 20.26 and 24.30, while the former had Q  ×  f  ~ 60, 983 GHz and the latter had Q  ×  f  ~ 95,300 GHz. The grain growth exponent and activation energy obtained from the phenomenological kinetic equation indicated the growth process of ceramics. The grain growth of Zn-based ceramic was dominated by interfacial reactions and lattice diffusion. For the other one, the grain growth mechanisms were grain boundary diffusion and lattice diffusion at high temperatures. The grain growth progress of them both affected by lattice diffusion. The growth process of ZnO-ZrO 2 -Ta 2 O 5 ceramics was faster than that of CoO-ZrO 2 -Ta 2 O 5 ceramic. However, the grains were overgrown and grew slowly at 1425°C and 1450°C, which was caused by the excessive high temperature.