Preparation and electrical properties of copper-nickel manganite ceramic derived from mixed oxalate

Cu0.3Ni0.66Mn2.04O4 negative temperature coefficient (NTC) ceramic was prepared using mixed oxalate-derived oxide powder. The mixed oxalate was synthesized by milling a mixture of copper acetate, nickel acetate, manganese acetate and oxalic acid at room temperature. The spinel-structured oxide powder was obtained by calcining the mixed oxalate in air at 800 °C for 2 h. The oxide powder compact was sintered at a relatively low temperature of 1100 °C for 2.5 h, attaining a relative density of ∼98%. The sintered ceramic had a specific resistivity ρ25 °C of 63.3 Ω cm and the thermal constant B25/50 of 2740 K, and exhibited much reduced shift in electrical resistivity of ∼5% after annealing at 150 °C for 500 h in air. The difference in the electrical property of the as-prepared ceramic is attributed to the fine-grained microstructure and the lower sintering temperature used in the present study.