Abstract: Nanoparticles of a mixed oxide precursor are reduced to form particles of a anostructured metastable alloy having a majority metal and a minority metal. Additional heating enriches the surfaces of the particles with respect to the minority metal, thus forming a coating on the particle core. This coating has a higher atomic ratio of minority to majority metal than found in the precursor. The nanostructured metastable alloys may then be oxidized to form nanoparticles having a coating of the oxide of the minority metal and a core of the majority metal or an oxide of the majority metal. The majority metal may be, for example, copper. The minority metal may be, for example, cobalt.