Influence of Ti element on the electrical properties of negative temperature coefficient ceramics in Ca–Ce–Ti–W–O system

In the present paper, the effects of TiO₂ addition on the electrical properties of negative temperature coefficient (NTC) ceramics in Ca–Ce–Ti–W–O system are elaborately investigated. The semiconducting material was produced by solid state reaction method at 1300 °C in atmosphere. The phase composition, microstructure, and electrical properties of the compounds are studied. The X-ray diffraction analysis shows that the major phase presented in the as sintered samples is CaWO₄-type scheelite compound together with a small amount of cubic Ca₂TiWO₇ compound. The existence of Ce and Ti in CaWO₄-type scheelite phase and the presence of \({\text{Ti}}^{3 + }\) are confirmed by energy dispersion spectrum (EDS) and X-ray photoelectron spectroscopy (XPS) analysis, respectively. Electrical properties are studied over the temperature range of 40–600 °C, results reveal that the resistivity at 50 °C ρ_50 °C shows a V-type curve with the increase of Ti content and the material constant B_300/600 °C varies from 4500 to 6000 Kelvin (abbreviated as K hereafter). Polaron theory reveals that the increase of conductivity with Ti content can be attributed to the hopping mechanism and consequently, the conductivity is effectively tuned by the Ti content.