FeCo nanoalloy formation by decomposition of their carbonyl precursors

Abstract

In this paper we describe the synthesis of iron and cobalt nanoalloys by the co-decomposition of iron and cobalt carbonyl precursors in the presence of polystyrene as a surface stabilizing agent. In order to prevent the preferential aggregation of metal atoms in the iron–cobalt nanoalloys, which results in phase segregation, the decomposition kinetics of the Fe(CO)₅ and Co₂(CO)₈ precursors had to be firmly established and controlled. The kinetics of cobalt cluster formation have been thoroughly investigated and documented, but data for Fe(CO)₅ decomposition are relatively scarce. To fully explore the kinetic characteristics of the formation of iron nanoclusters, initial Fe(CO)₅ concentrations and reaction media solvents were varied and hence reaction order and rate constants were established. Our results suggest that this decomposition is a higher-order process (not first-order as previously assumed), with a complicated intermediate mechanism, which has been postulated and experimentally verified. By using this kinetic data, we were able to predict the necessary conditions for the in situ creation of new iron–cobalt nanoalloys using carbonyl precursors. Equal initial concentrations of both precursors generated nanoalloys with a crystalline core–shell dense morphology, while precursor concentrations corresponding to initial equal rates of decomposition generated polycrystalline nanoalloys with a diffuse morphology.