Microstructure and dielectric characteristics of Nb2O5 doped BaTiO3-Bi(Znl/2Til/2)O3 ceramics for capacitor applications

Abstract

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 0.5wt.%–3.0wt.%. The 0.8BT-0.2BZT ceramics doped with 1.5wt.% Nb2O5 was found to possess a moderate dielectric constant (ε=1170) and low dielectric loss (tanδ=1%) at room temperature and 1kHz 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 26.5nF, with dielectric loss tanδ of 0.9% and electrical resistance of 4.50×1011Ω at room temperature, leading to a high time constant of 11,900s, decreasing to 175s 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 0.2mΩ at 2MHz, much lower than that of the DC Bus Capacitor Bank for the automotive inverters (where the desired characteristic is <3mΩ). All these characteristics of the newly developed MLCC will benefit the high temperature and high power capacitor applications.