Preparation Of High Dielectric Constant'Y5V'Ba (Ti,Zr) O₃-based Ceramics

BaTiO3 relaxor ferroelectrics are of great interest for multilayer ceramic capacitor (MLCC) and tunable microwave device applications due to high permittivity, low dielectric loss, and high dielectric tenability. The Y5V-type ceramics have demonstrated a higher temperature coefficient of capacitance. In order to meet the EIA Y5V specification, depressors and shifters are doped to substitute A site or B site. Currently, the properties of ceramics prepared by traditional method were not significantly improved, because the doping concentration entered into lattice is limited. In this paper, a dopant added to the process of the Ba(Ti, Zr)O3-based ceramics in two stages. Through the regulation of the sintering process and dopants doping style, concentration, species, the Ba(Ti, Zr)O3-based'Y5V' ceramics with high dielectric and low dissipation were prepared. On this basis, a one-step Sol-gel method was developed to synthesis this materials, which will simplify the production process and obtain the powders with high purity, uniformity, and nanosize. The powders and ceramics which synthesize by one-step sol-gel method will reduce component size with increasing the volumetric efficiency of the MLCCs by decreasing the dielectric layer thickness.The research content, see as follows:1,A distinct diversification of the microstructures and dielectric character of Ba(Ti0.86Zr0.14)03 ceramics doped with Nb2O5 in different. doping style were observed. Adjustment adapted ratio of Nb2O5 by adding the dopant before and after synthesis of BZT main crystal phase can control the amount of niobium incorporation in BTZ lattice, thus the process can limit the grain size and enhance the relative permittivity of the BTZ ceramics. When this doping method met a definite proportion (Nb amount doped before main crystal phase synthesis in aggregate is 43%), we obtained the sample with a high dielectric constant over 20000, low dielectric loss lower then 0.40% at room temperature, the dielectric strength 3.64 kV/mm under AC field. Besides, increasing the concentration of doped niobium resulted in decreasing dielectric loss of ceramics, and also made the dielectric constant and dielectric strength increasing at first and then decreasing. When the Nb concentration was 0.470 wt%, the ceramics met the EIA Y5V specifications and theεmax was greater than 21000.2,Different amount of ZnO or Nd2O3 doped ceramics and co-doped ceramics were prepared by solid state method at low sintering temperature. Compared to the independent doping behavior, the co-doped ceramics with small and uniform size reached high dielectric constant between the two independent doped ceramics. When the ZnO amount was 0.20 wt% and the Nd2O3 amount was 0.35 wt%, the ceramics met the EIA Y5V specifications and theεmax was greater than 15400.3,Ba(Ti, Zr)O3 ceramics were prepared by a one-step sol-gel method. When the calcining temperature increased from 900℃to 1100℃, impurity phases decreased gradually, and until there is no impurity phase. But the grain size increased as the increasing of the calcining temperature and sol pH. The sol pH also made the dielectric constant increase at first and then decrease. At pH 2.5, theεmax was 21100, the dielectric loss was 0.51%, and the ceramic met the EIA Y5V specifications.