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.
► Dy/Tm co-doping method in BaTiO3 was suggested to improve electrical properties and temperature stability simultaneously. ► We examined these properties in terms of microstructural analysis and substitution rate. ► Increase of Dy2O3 addition enhanced dielectric constant. ► Increase of Tm2O3 addition enhanced temperature stability. ► Improved electrical properties and temperature stability through Dy/Tm co-doping were deduced from formation of electrons and core–shell structure.