Microstructure and thermal properties of dysprosium and thulium co-doped barium titanate ceramics for high performance multilayer ceramic capacitors

The co-doping characteristics on microstructure and thermal properties of barium titanate (BaTiO₃) were investigated to elucidate formation of core-shell structure by dysprosium (Dy) and thulium (Tm) addition in the BaTiO₃-Dy₂O₃-Tm₂O₃ system. The dielectrics co-doped with 0.7 mol% Dy₂O₃ and 0.3 mol% Tm₂O₃ had the dielectric constant up to 2200 as a function of temperature, which was 30% higher than that of specimen containing only Tm₂O₃ at the room temperature. It could be explained by the fact that the increase of Dy₂O₃ addition contributed to the improvement of dielectric constant. On the other hand, the rapid diffusion rate of Dy³⁺ ions in BaTiO₃ showed an adverse effect on temperature stability caused by destruction of core-shell. As the compensation for shell expansion in BaTiO₃, the reinforcement of the core-shell structure through the addition of Tm₂O₃ was confirmed by TEM-EDS analysis and attributed the temperature coefficient of capacitance (TCC) in a reliability condition (−55 °C to 125 °C, △C = ±15% or less). The enhanced electrical properties and temperature stability could be deduced from the generation of electrons and the formation core-shell structure in co-doped BaTiO₃ system respectively.