Preparation routes and electrical properties for Ni_0.6Mn_2.4O₄ NTC ceramics

Ni_0.6Mn_2.4O₄ negative temperature coefficient ceramics were prepared by using solid-state coordination reaction and traditional solid-state methods, their structures and properties were characterized by using scanning electron microscopy, powder X-ray diffractometer and temperature dependent resistivity test. For solid-state reaction powders, the calcination temperature necessary for formation of the spinel phase was 1000 °C, which is 300 °C higher than that of solid-state coordination reaction powders. Regardless of preparation routes, the ceramics were crystallized in a single cubic spinel structure when the sintering temperature was lower than or equal to 1150 °C, Mn₃O₄ impurity phase was detected when the sintering temperature raised to 1200 °C. Having higher densities and bigger grain sizes, the solid-state coordination reaction samples had smaller room temperature resistivities and larger B_25/50 values as compared with those of solid-state samples.