Preparation and electrical properties of Ni_0.6Mn_2.4-xTi_xO₄ NTC ceramics

In this paper, spinel-type negative temperature coefficient (NTC) ceramics with general composition Ni_0.6Ti_xMn_2.4-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 Mn on the B-sites.