Impedance analysis of Nb2O5 doped BaTiO3-Na0.5Bi0.5TiO3 ceramics

BaTiO₃-based MLCC materials were limited for high temperature applications (temperature range up to 200°C), due to their low Curie temperatures. The addition of Na_0.5Bi_0.5TiO₃(NBT) component in BaTiO₃(BT) based ceramics was found to increase the Curie temperature, without sacrificing the dielectric constant. The Curie temperature was reported to increase from 125°C to 156°C with addition up to 10mol%, making it possible to satisfy the X8R or X9R criterions. In addition, the small amount of Nb₂O₅ dopant in the system leads to a diffused dielectric maxima and improved temperature stability. The NBT-BT with 2wt% Nb₂O₅ addition was found to exhibit a core-shell structure, while maintaining the dielectric constant at about 2500. To analyze the electrical microstructure variation, the obtained impedance data was fitted by a 4RC equivalent circuit, corresponding to the core, shell, grain boundary, and ceramic/electrode interface regions. All the electrical properties, including the capacitance, activation energy, and conductivity could be well explained by using this equivalent circuit.