Preparation of ultra-fine cobalt–nickel manganite powders and ceramics derived from mixed oxalate

Co0.30Ni0.66Mn2.04O4 negative temperature coefficient ceramics were derived from mixed oxalate Co0.30Ni0.66Mn2.04(C2O4)3·nH2O. The mixed oxalate was synthesized by milling a mixture of cobalt acetate, nickel acetate, manganese acetate, and oxalic acid at room temperature. An ultra-fine Co0.30Ni0.66Mn2.04O4 powder was obtained by calcining the mixed oxalate in air at 800 °C for 3 h. The oxide powder compact was sintered at a relatively low temperature of 1100 °C for 5 h, achieving a relative density of ∼98%. The specific resistivity ρ25 °C and the thermal constant B25/85 °C were 765.2 Ω cm and 3604 K, respectively. The resistance drift after aging at 150 °C for 500 h was 1.5%.