Abstract: Nano-powders of Co_0.8Mn_0.8Ni_0.9Fe_0.5O₄ NTC (Negative Temperature Coefficient) thermistor materials were prepared by co-precipitation method with NH₄HCO₃ as precipitator. The effects of calcination temperature on the material phase were studied. The influences of different sintering processes on the microstructure and thermal sensitive characteristics of NTC thermistor materials were investigated. The samples were characterized by XRD, TG/DTA, FT-IR, SEM, and Laser Particle Size Analyzer. The results show that the powders calcined at 750℃ are single spinel, the grain size of the powders is about 32.1nm, and the particle size is about 50-100nm. The samples possess better electrical properties: ρ_25℃=1183Ω·cm, B_25/50=3034K under the process conditions of constant temperature 840℃ and 1200℃ for 2h respectively, the heating and cooling rate of 1℃/min. It is found that proper sintering process can effectively improve the microstructure and thermal sensitive properties of the NTC thermistor materials. According to the calculation from the slope of lnρ-1/T curves, the activation energy is about 0.26eV.

Key words: NTC thermistor, nano-powders, co-precipitation, resisitivity