Room-temperature synthesis of monodisperse mixed spinel (CoxMn1−x)3O4 powder by a coprecipitation method

Spinel oxide Co 3 O 4 has traditionally been synthesized by thermal decomposition of cobaltous salts at temperatures of 250-900°C under oxidizing conditions. Here, we report a solution synthesis route that yields mixed spinel oxide (Co x Mn 1–x ) 3 O 4 at room temperature in air. (Co 0.75 Mn 0.25 ) 3 O 4 solid solutions were synthesized by coprecipitation and oxidation of Co(OH) 2 and Mn(OH) 2 from mixed aqueous solutions of Co- and Mn-salts. The spinel oxide phase was stabilized by crystallization of Mn 3 O 4 resulting from the oxidation of Mn(OH) 2 in the mother liquor. While undoped Mn 3 O 4 is tetragonal, the (Co 0.75 Mn 0.25 ) 3 O 4 solid solution has a cubic symmetry due to the reduced Mn3+ concentration. The resulting powder is spherical with an average particle diameter of ca. 0.1 µm and a narrow size distribution. Transmission electron microscopy (TEM) showed that individual particles are nearly single crystalline but consist of a mosaic of multiple nanocrystallites. This observation supports an aggregation mechanism of formation for the nearly monodispersed particles.