Ni0.79Mn2.21O4 ceramics were prepared using the mixed-oxide method. All specimens displayed the typical XRD patterns of a single-phase cubic polycrystalline structure. The average grain size of the specimen sintered at 1200 oC was approximately 6.65 μm. All specimens exhibited the typical NTC thermistor characteristic where the electrical resistance exponentially decreases with an increase in temperature. The conduction process can be explained well by the nearest neighbor hopping (NNH) mechanism. The NTC property, activation energy, B25/50 constant and resistivity at room temperature of the Ni0.79Mn2.21O4 specimen sintered at 1150 oC were -4.2%/oC, 4024 K, 0.329 eV and 3360 Ω·cm, respectively. These values are good enough to be applied to NTC thermistor devices.

Keywords: Ni-Mn oxide, Sintering temperature, Structural properties, Electrical properties.