Microstructure and electrical properties of Mn2.25-xNi0.75CoxO4 thermistor ceramics

A series of composite of the negative temperature coefficient (NTC) powders of Mn2.25-xNi0.75CoxO4 (0.8 <= x <= 1.2) 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 degrees C, their characteristic parameters B-25/50 value are found to be in the range of 3487K to 4455K and their electrical resistivities rho(25 degrees C) are 1998 Omega.cm to 203617 Omega.cm. The B25/50 value and rho(25 degrees 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.