Preparation of Ultra‐Fine Nickel Manganite Powders and Ceramics by a Solid‐State Coordination Reaction

Abstract

A solid‐state coordination reaction was adopted to prepare negative temperature coefficient ceramics. A mixed oxalate NiMn 2 (C 2 O 4 ) 3 ·6H 2 O, a coordination compound, was synthesized by milling a mixture of nickel acetate, manganese acetate, and oxalic acid for 5 h at room temperature. An ultrafine NiMn 2 O 4 powder was obtained by calcining the mixed oxalate in air at 850°C for 2 h. Ceramics with a relative density of more than 97% were achieved by sintering powder compacts at a temperature as low as 1050°C for 5 h. The specific electrical resistivity ρ 25°C and the thermal constant B 25°/85°C were 2174 Ω·cm and 3884 K, respectively. The drift of the resistivity after aging at 150°C for 1000 h was 3.0%.