Effect of sintering temperature on structural and electrical properties of Mn0.55Fe1.25Cu2Ni2.2O4+δ NTC thick film

Mn0.55Fe1.25Cu2Ni2.2O4+δ glass-free thick films with negative temperature coefficient (NTC) character were fabricated on Al2O3 substrate by screen printing technology. The microstructural, electrical parameters, and cation distribution of materials varied with the slight change in sintering temperature (1000 °C, 1025 °C, 1050 °C) were investigated. All the thick film samples showed spinel structure of its main phase. CuAl2O4 phase was found when the sintering temperature was above 1025 °C, which is of practical importance for copper-containing thermal-sensitive materials bonding Al2O3 substrate. Both the room-temperature resistance R25 and material constant B value increased as temperature increased, R25 in the range of 17.3–125 kΩ, and B lying in the range of 2824–3074 K. Such feature was attributed to the redistribution of the multivalent state Mn, bivalence Fe and Cu cations with increasing sintering temperature. The optimal sintering temperature was 1000 °C due to its pure phase, best crystallinity, and lowest B value (2824 K), which was a good candidate for temperature monitoring and control in a relative widen temperature range.