Influence of the electric field and annealing temperature on flash-sintered (Mg_1/3Nb_2/3)_0.05Ti_0.95O₂ ceramics

(Mg, Nb) co-doped TiO₂ colossal dielectric ceramics were successfully prepared at 1200 °C for 24 min. The effects of different electric field on phase structure, microstructure and dielectric properties have been systematically studied. All the flash sintered samples were pure rutile TiO₂ structure, and no second phase was produced. With the increase of electric field, the dielectric constant (at 1 kHz) firstly increases and then decreases. When the electric field is 550 V/cm, the dielectric properties (ε′ ≈ 6.0 × 10⁵, tanδ ≈ 0.73) of the ceramic sample are the best. Flash sintered samples were annealed at different temperatures (800–1000 °C) in order to reduce dielectric loss. As the annealing temperature increases, the dielectric constant decreases gradually. When the annealing temperature is 800 °C, the dielectric constant of the ceramic sample is about 7.1 × 10⁴ and the dielectric loss is about 0.37 (twice reduced) at 1 kHz. Impedance spectroscopy (IS) data indicated that ceramics consist of semi-conductive grains and insulated grain boundaries. This good dielectric property was attributed to the internal barrier layer capacitance (IBLC) effect.