Crystallite Size Controls the Crystal Structure of Cu₆₀Pd₄₀ Nanoparticles

Structurally disordered (Cu type of structure) or ordered (CsCl type of structure) modifications of intermetallic Cu 60 Pd 40 nanoparticles can be synthesized by co-reduction of Cu- and Pd-acetylacetonate using LiBEt 3 H in THF or annealing in tetradecane, respectively. It is shown by X-ray diffraction, transmission electron microscopy, selected area electron diffraction, differential centrifugal sedimentation, and thermal analysis that the formation of the ordered or the disordered modification depends on the crystallite size of the nanoparticles rather than on temperature. Crystallites smaller than ∼20 nm form the disordered modification of Cu 60 Pd 40, whereas crystallites larger than 20 nm prefer the ordered modification.