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

Spinel oxide Co3O4 has traditionally been synthesized by thermal decomposition of cobaltous salts at temperatures of 250-900 degrees C under oxidizing conditions. Here, we report a solution synthesis route that yields mixed spinel oxide (CoxMn1-x)(3)O-4 at room temperature in air. (Co0.75Mn0.25)(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 Mn3O4 resulting from the oxidation of Mn(OH)(2) in the mother liquor. While undoped Mn3O4 is tetragonal, the(Co0.75Mn0.25)(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 mu m 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.