Effect of Al2O3 addition on the microstructure and the electrical stability of MnNiCoO4 NTC thermistors

The effect of partial substitution of Al for Co on the electrical stability of MnNiCo1-xAlxO4 (0 ≤ x ≤ 0.20) negative-temperature-coefficient (NTC) thermistors was studied. The Al substitution decreased the grain size and the density. The resistivity of the thermistors increased with increasing Al content. In particular, the substituted Al led to a significant decrease in the resistance change of the NTC thermistors after soldering or thermal shock. This demonstrates that the Al-substituted MnNiCo1-xAlxO4 NTC thermistors have good electrical stability in comparison to MnNiCoO4 thermistors. We, therefore, believe that Al substitution is fairly effective for achieving stable, high performance, NTC thermistors.