Disappearance and recovery of colossal permittivity in (Nb plus Mn) co-doped TiO2

We investigate the effects of doping and annealing on the dielectric properties of metal ions doped TiO2 ceramics. Colossal permittivity (CP) above 10(4) was observed in single Nb ion doped TiO2, which was dominated by electron transport related interfacial polarization. Moreover, the CP can be dropped to 120 when simultaneously introducing Mn ion into the sample. The disappearance of CP behaviors maybe due to the multivalence of Mn which would inhibit the reduction of Ti4+ to Ti3+, and thus reduce delocalized electrons. Interestingly, the CP was recovered for the (Nb + Mn) co-doped TiO2 after post-sintering heat treatment in N-2 atmosphere. The recovery of CP in the sample after annealing can be ascribed to the semiconducting grain and the insulating grain boundary, according to impedance spectroscopy. We therefore believe that this work can help us understand the mechanism of CP from a new perspective.