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

Abstract

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 ρ50 °C shows a V-type curve with the increase of Ti content and the material constant B300/600 °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.