Comparison of structure and electrical properties of vacuum-sintered and conventional-sintered Ca1-xYxCeNbWO8 NTC ceramics

The effects of vacuum sintering and conventional sintering on the structure and high-temperature electrical properties of Ca1-xYxCeNbWO8 ceramics have been comparatively studied. X-ray diffraction (XRD) result shows that the conventional-sintered ceramic is a single CaWO4 phase with a scheelite structure, whereas the vacuum-sintered ceramics are composed of a major CaWO4 phase with scheelite structure and a minor CeNbO4 phase with fergusonite structure. The grain size of the conventional-sintered Y-doped ceramics is smaller than that of the undoped samples. The grain size of the vacuum-sintered samples increases firstly and then decreases with increasing the Y concentration. The activation energy of the conventional-sintered and vacuum-sintered ceramics all decreases with increasing the Y content. The activation energy of the vacuum-sintered samples is smaller than that of conventional-sintered samples at the given compositions. The change of activation energy should be attributed to the variation of Ce3+ ion concentration.