Preparation Of ZnNb₂O₆ Powder By Co-precipitation And Dielectric Property Of Sintered Ceramics

The Zn Nb2O6 ceramics have received much scientific attention because it’s excellent microwave dielectric properties and the sintering temperature is only 1200℃. Currently, the research of Zn Nb2O6 ceramics has been mainly on improving the dielectric properties, but the results achieved is not excellent. In the course of previous study on the niobium phase Zn Nb2O6, the powders were prepared by the conventional solid state method. The solid state reaction have the problems of large grain size, broad particle size distribution and impurity, more over the calcining temperature is high. Therefore, it is a very important issue to investigate the new synthesis processes for preparing the fine niobate powders with small gain size, narrow particle size distribution and high purity. In the present, the Zn Nb2O6 powders were synthesized by Co-precipitation in this paper, and the systemic investigations were focused on the effects of different parameters on the phase and microstructure of the powders and the bulk density and dielectric behaviors of ceramics.The single-phase Zn N2O6 powders were successfully synthesized at 750℃ by Co-precipitation from the starting materials: Zn(NO3)2·6H2O, Nb2O5, HF and the precipitant: NH3·H2O. Results showed that the p H value has a little effect on the powder phase, when the p H value was 8, we can get the Zn Nb2O6 phase but less Zn3Nb2O8 impurity phase because of the heterogeneous precipitation of zinc niobate; With the increase of p H value, the particle size decreased.The reaction temperature and solution concentrations have obvious effects on the phase and the grain sizes of Zn Nb2O6 powders, but not obvious on the morphology. TEM photographs revealed that increase the reaction temperature, the particle size decreased first and then increased slightly with the aggregation, we could get the best powders at 25℃;When the solution concentration was 0.5mol/L, the powders presented the regularly rod-like shape and its sizes were about 160 nm. The optimum synthesis processes were: p H value was 10, the reaction temperature was 25℃, the solution concentration was 0.5mol/L and the calcined temperature was 750℃.We could get the single Zn Nb2O6 phase when the ceramics were sintered using the compound of powders synthesized by Co-precipitation and solid reaction. With the increasing of X(wt%)and sintering temperature, The grain size increased, while density decreased. When the X was 20 to 30, a few of grains grew unusually, and the dielectric constant and the quality factor decreased; As a whole, it can be obtained that the maximal dielectric constant and the quality factor were 24.2 and 78600GHz; However, the minimal dielectric loss is-55.2×10-6/℃when X is 0,which show good temperature stability.Compared with the conventional sintering, Microwave sintering method can decrease the sintering temperature by about 100℃and the sintering time by about 1.5h,which can not only effectively inhibit Zn evaporation but also get excellent microstructure; we can get the great dielectric properties: er=24.8,Q×f=78156GHz,τf=-52.1×10-6/℃,when sintered at 1050℃by microwave sintering method.