Microstructure and dielectric characteristics of Nb2O5 doped BaTiO3-Bi(Znl/2Til/2)O3 ceramics for capacitor applications
The effects of Nb2O5 addition on the dielectric properties and phase formation of 0.8BaTiO3-0.2Bi(Znl/2Til/2)O3 (0.8BT-0.2BZT) ceramics were investigated. The desired perovskite phase was achieved with Nb2O5 doping levels being in the range of 0.5 wt.%-3.0 wt.%. The 0.8BT-0.2BZT ceramics doped with 1.5 wt.% Nb2O5 was found to possess a moderate dielectric constant (ε = 1170) and low dielectric loss (tanδ = 1%) at room temperature and 1 kHz frequency, showing a flat dielectric behavior over the temperature range of −55 °C-200 °C. Based on this composition, the X9R-MLCC (multilayer ceramic capacitor) with Ag0.7-Pd0.3 electrode was sintered at 1060 °C. The optimized capacitance of the MLCC is 26.5 nF, with dielectric loss tanδ of 0.9% and electrical resistance of 4.50 x 1011 Ω at room temperature, leading to a high time constant of 11,900 s, decreasing to 175 s at 200 °C, being one order higher than those of commercial X7R MLCC. In addition, the equivalent series resistance (ESR) was found to be on the order of 0.2 mΩ at 2 MHz, much lower than that of the DC Bus Capacitor Bank for the automotive inverters (where the desired characteristic is <3 mΩ). All these characteristics of the newly developed MLCC will benefit the high temperature and high power capacitor applications.