Giant dielectric properties of terbium and niobium co-doped TiO2 ceramics driven by intrinsic and extrinsic effects

Giant dielectric properties (GDPs) of complex oxides have been widely investigated because of their potential applications in ceramic capacitors. This study describes the improvement in three crucial factors of the GDPs of TiO2 by co-doping it with Tb and Nb ions. (Tb0.5Nb0.5)xTi1-xO2 (TNTO) ceramics with x = 1–5% were prepared using a conventional mixed-oxide method. The ceramics exhibited a highly compact microstructure and microwave dielectric phases of Tb2Ti2O7 and TbNbTiO6. Notably, the temperature dependence of the dielectric permittivity (ε′) (∆ε′(T)/ε′30℃) was less than |±15%| from −60 to 210 ℃. Furthermore, the TNTO ceramics exhibited extremely low tanδ values (0.006–0.011) and high ε′ values (4.7–5.3×104) at 1 kHz. The tanδ values at 200 °C were particularly low (0.033–0.057). Impedance spectroscopy revealed the presence of semiconducting grains, and the enormous resistivity of the grain boundaries and microwave dielectric phase particles. The GDPs are primarily caused by both intrinsic and extrinsic effects. The intrinsic effect was due to the formation of defect clusters (i.e.,Nb25+Ti3+XTi(X=A3+/Ti3+/Ti4+)−Tb23+V0••Tⅈ3+, 2TbTi′−VO••, TbTi′−NbTi•, 3TiTi′−VO••−NbTi•, and TiTi′−VO••−TiTi′), whereas the extrinsic effect resulted from the internal barrier layer capacitor microstructure. The presence of microwave dielectric phases can cause a decrease in tanδ and improve the temperature stability of ε′.