In this paper, we investigated the effect of Co content on the microstructural and electrical properties of Ni0.79Mn2.21-xCoxO4 (x=0 to 0.25) specimens. Solid-state reaction was used to prepare the bulk specimens. XRD (X-ray diffraction) patterns showed that all compositions had a cubic spinel phase. As a result of the microstructural properties, FE-SEM(field-emission scanning electron microscopy) analysis showed a dense structure, and the mean grain size increased from 5.24 μm to 7.33 μm with an increase of Co content from x=0 to 0.25. All specimens exhibited the typical NTC thermistor characteristics as the electrical resistance exponentially decreased with increasing temperature. The resistivity and the B-value of Ni0.79Mn1.96Co0.25O4 were 2959 Ω·cm and 3719, respectively.
