Molten Salt Synthesis Prepared Niobium-zinc-based Microwave Dielectric Ceramics Structure And Performance Research

microwave dielectric ceramic is developed in recent years. It exhibits high quality factors (Q×f) and adjustable temperature coefficients of resonsant frequency. Due to its hingh sintering temperature (1150℃), it is difficult to realize co-fired with Ag or Cu. So it is essential to investifate its characteristics and low-temperature sintering. In this article, powders of pure ZnNb2O6 were prepared by molten salt methord. Then we lowered the sintering temperature of ZnNb2O6 by doping CuO. At last we joined TiO2 to modified ZnNb2O6 propertis, which has positive temperature coefficients of resonsant frequency.KCl-NaCl-ZnCl2 was used as molten salt. The mass ratio of molten salt and raw material is 1:1. Powders of pure ZnNb2O6 ceramic were synthesized at 650℃, which was reduced by 200℃relative to solid phase method. ZnNb2O6 powders preferably grow along special direction, and appear strip or rod like. ZnNb2O6 powders calcined at 650℃have narrow particle size distribution. Median size D50=5.31μm. Grain grows and particle size increases with the increase of the calcining temperature.ZnNb2O6 powders synthesized by molten salt method at 650℃were sintered by doping CuO as addition agent. It is showed that:The ZnNb2O6 has the largest bulk density (5.4445g/cm3), which was doped lwt% CuO and sintered at 1000℃. The sintering temperature was lowered by 150℃, relative to the traditional method. With less than 1wt% additive, the main crystalline phase is columbite ZnNb2O6. With more than 2wt% additive, Cu0.5Zn0.5Nb2O6 is found as the second phase in the samples. We found that ZnNb2O6 ceramic doped 1wt% CuO and sintered at 1000℃exhibits good dielectric properties:εr=22.56, Q×f=22 318 GHz,τf=-86.08 ppm/℃.ZnNb2O6 powders was doped CuO and added TiO2 to modify properties, which were synthesized at 650℃by molten salt method. And ZnNb2O6-1.75TiO2 ceramic was prepared. The results showed that with 4wt%,CuO additive, ZnNb2O6-1.75TiO2 has the largest bulk density 5.024g/cm3, which was sintered at 1000℃In these samples sintered at 1000℃:With lwt% CuO additive, there are ZnNb2O6 and TiO2 remains;With 4wt% CuO additive, the pure ZnTiNb2O8 was obtained;With 8wt% CuO additive, the second phase (Cu0.5Zn0.5)Nb206 was synthesized.We found that 4wt% CuO doped ZnNb2O6-1.75TiO2 ceramic sintered at 1000℃exhibits good dielectric properties:εr=44.2; Q×f=19 654GHz;τf=17.4ppm/℃.