Colossal Permittivity Characteristics of (Nb, Si) Co-Doped TiO 2 Ceramics.

(Nb 5+ , Si 4+ ) co-doped TiO 2 (NSTO) ceramics with the compositions (Nb 0.5 Si 0.5 ) x Ti 1-x O 2 , x = 0, 0.025, 0.050 and 0.1 were prepared with a solid-state reaction technique. X-ray diffraction (XRD) patterns and Raman spectra confirmed that the tetragonal rutile is the main phase in all the ceramics. Additionally, XRD revealed the presence of a secondary phase of SiO 2 in the co-doped ceramics. Impedance spectroscopy analysis showed two contributions, which correspond to the responses of grain and grain-boundary. All the (Nb, Si) co-doped TiO 2 showed improved dielectric performance in the high frequency range (>10 3 Hz). The sample (Nb 0.5 Si 0.5 ) 0.025 Ti 0.975 O 2 showed the best dielectric performance in terms of higher relative permittivity (5.5 × 10 4 ) and lower dielectric loss (0.18), at 10 kHz and 300 K, compared to pure TiO 2 (1.1 × 10 3 , 0.34). The colossal permittivity of NSTO ceramics is attributed to an internal barrier layer capacitance (IBLC) effect, formed by insulating grain-boundaries and semiconductor grains in the ceramics.