Effect of partial substitution of Mg for Co in Mn1.4Ni1.2Co0.4O4NTC thermistors on electrical stability

Sintered Mn1.4Ni1.2Co0.4 - x MgxO4 (0 <= x <= 0.25) samples were thermal constrained by heating at 850 degrees C followed by air cooling. As-sintered and thermal constraint samples were composed of Mn- and Ni-rich phases with a cubic spinel structure. The substituted Mg suppressed the separation of Ni-rich phase in a Mn1.4Ni1.2Co0.4 - x MgxO4 solid solution and resulted in a more stable spinel structure. In particular, the substituted Mg led to a significant decrease in the resistance drift of the Mn1.4Ni1.2Co0.4 - x MgxO4 NTC thermistors after thermal constraint. This indicates that the Mg substituted Mn1.4Ni1.2Co0.4 - x MgxO4 NTC thermistors have good electrical stability in comparison with the Mg-free Mn1.4Ni1.2Co0.4O4 thermistors. We strongly recommended the substitution of Mg for Co in Mn-Ni-Co-O NTC thermistors for stabilizing their resistivity drift, i.e., ageing.