Origin(s) of the apparent colossal permittivity in (In1/2Nb1/2)xTi1−xO2: clarification on the strongly induced Maxwell–Wagner polarization relaxation by DC bias

Abstract

The effects of DC bias on the dielectric and electrical properties of co-doped (In_1/2Nb_1/2)_xTi_1−xO₂ (IN-T), where x = 0.05 and 0.1, and single-doped Ti_0.975Nb_0.025O₂ ceramics are investigated. The low-frequency dielectric permittivity (ε′) and loss tangent of IN-T ceramics with x = 0.05 and 0.1 are greatly enhanced by applying a DC bias at 40 and 20 V, respectively, whereas the relatively high-frequency ε′ remains unchanged. The induced low-frequency Maxwell–Wagner polarization completely vanishes by immediately applying no DC bias. After overload limited measurement, this polarization permanently emerges without DC bias, whereas the primary polarization remains unchanged. Using combined Z′′ and M′′ spectroscopic plots, it is found that the strongly induced-polarizations are contributed from the combination effects of the sample–electrode contact and resistive outer surface. Very high performance of the colossal permittivity in IN-T ceramics is attributed to the formation of a resistive outer-surface layer and insulating grain boundaries. These results not only provide important insights into the origins of the colossal dielectric response in the IN-T ceramic system, but are also important for deciding the doping conditions of TiO₂-based materials for practical applications.