Microstructure and Electrical Properties of Mn<SUB>2.25-x</SUB>Ni<SUB>0.75</SUB>CoxO<SUB>4</SUB> Thermistor Ceramics

A series of composite of the negative temperature coefficient (NTC) powders of Mn2.25-xNi0.75CoxO4 (0.8&lex&le1.2) materials were prepared via solid-state method. The particle size of calcined powders, ceramics phase structure, morphology and electrical properties were characterized by laser particle size analyzer, XRD, SEM and electrical measurements, respectively. The results show that when the Mn2.25-xNi0.75CoxO4 ceramics sintered at 1130-1230°C, their characteristic parameters B25/50 value are found to be in the range of 3487 K to 4455 K and their electrical resistivities ρ25°C are 1998 Ω·cm to 203617 Ω·cm. The B25/50 value and ρ25°C first increases and then decreases as the Co content increases. This means that electrical resistivity and B value of Mn2.25-xNi0.75CoxO4 ceramics could be adjusted to the desired values and this ternary system can be considered as the advanced semi-conducting materials for NTC thermistor applications.