Colossal Permittivity Characteristics of (Nb, Si) Co-Doped TiO2 Ceramics

(Nb5+, Si4+) co-doped TiO2 (NSTO) ceramics with the compositions (Nb0.5Si0.5)(x)Ti1-xO2, 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 SiO2 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 TiO2 showed improved dielectric performance in the high frequency range (>10(3) Hz). The sample (Nb0.5Si0.5)(0.025)Ti0.975O2 showed the best dielectric performance in terms of higher relative permittivity (5.5 x 10(4)) and lower dielectric loss (0.18), at 10 kHz and 300 K, compared to pure TiO2 (1.1 x 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.