Effect of Ta2O5 and Nb2O5 Dopants on the Stable Dielectric Properties of BaTiO3–(Bi0.5Na0.5)TiO3-Based Materials

In this study, BaTiO3–(Bi0.5Na0.5)TiO3 ceramics with various amounts of Ta2O5 dopant were investigated for their ability to enhance high-temperature stability to meet X9R specifications. The results were compared to those for ceramics with the common Nb2O5 additive. The best composition appeared to be 0.9BaTiO3–0.1(Bi0.5Na0.5)TiO3 with 2 mol% Ta2O5 dopant sintered at 1215 °C, which had a dielectric constant of 1386, a tanδ value of 1.8%, temperature coefficients of capacitance (TCCs) of −1.3% and 1.2%, and electrical resistivities of 2.8 × 1012 and 1.5 × 1010 Ω·cm at 25 °C and 200 °C, respectively. Its microstructure consisted of fine equiaxed grains with a perovskite structure and an average grain size of 0.46 μm and some rod-like grains of second-phase Ba6Ti17O40 with a size of approximately 3.2 μm. The Ta2O5 dopant caused a reduction in the grain size and a slight increase in trapped pores. The temperature dependence of the dielectric constant flattened and the Curie point was dramatically suppressed with the addition of Ta2O5 dopant, leading to smooth dielectric temperature characteristics over a relatively broad temperature range. The X9R formulations and their dielectric properties were highly repeatable in this study.