Preparation and electrical properties of Ni0.6Mn2.4−xTixO4 NTC ceramics

Abstract

In this paper, spinel-type negative temperature coefficient (NTC) ceramics with general composition Ni0.6TixMn2.4−xO4 (x = 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6) were prepared by conventional solid-state reaction method. The effects of Ti content and sintering temperature on the phase composition, morphology and electrical properties were characterized by XRD, SEM and resistance–temperature measurements, respectively. The results showed that a single spinel structure of AB2O4 could be obtained at x ≤ 0.4, titanium oxide and manganese titanate were formed at x > 0.4. These samples could be sintered into relatively dense ceramics at a temperature of 1200 °C. For the samples sintered at 1200 °C, the grain size slightly increased when the Ti content increased from 0.1 to 0.3 and an abnormal grain growth was observed at x ≥ 0.4. The oversintering temperature decreased as the Ti content increased. The specific resistivity at 25 °C of the ceramics increased by adding Ti content and it increased sharply at x ≥ 0.4. The B values increased linearly with the increase of Ti content when the x value between 0.1 and 0.5, and then it decreased at x = 0.6. The variation of electrical properties is correlated with the occupation of Ti ions on the B-sites of the spinel structure and the decrease of Mn3+/Mn4+ on the B-sites.