Dielectric properties of nanocrystalline TiO2 prepared using spark plasma sintering

Ultra fine rutile powders (below 50 nm) were prepared via the sol-gel process and bulk type TiO2 specimens were fabricated using spark plasma sintering (SPS). The TiO2 specimen sintered at a low temperature (720∘C) exhibited a highly relative density (97%) and a nano-sized grain structure (200 nm). Dielectric properties of spark plasma sintered TiO2 specimens including dielectric constants (k) and losses (tan δ) were measured. The TiO2 specimen, obtained by SPS, showed a high dielectric constant (∼780) and a low tan δ (∼0.005), and a relaxation behavior at 1 MHz. After the subsequent annealing process of the TiO2 specimen in O2 flow, the dielectric constants remarkably decreased (k = 100s). These dielectric properties of nanocrystalline TiO2 specimens prepared by SPS were discussed in terms of space charges produced by the reduction of Ti4+ ions and crystallographic orientations of grains