Size and composition effects in polymer-protected ultrafine bimetallic PtxRu1-x (0 < x < 1) particles - art. no. 235407

Ultrafine PtxRu1-x particles (with 0 less than or equal tox less than or eq ual to1), synthesized by decomposition of organometallic precursors in the presence of a stabilizing polymer, are studied using both high-resolution t ransmission electron microscopy and wide-angle x-ray scattering techniques. In this paper, we focus on the influence of the size and the composition o n the atomic organization and structural features of Pt, Ru, and Pt-Ru part icles. It is shown that the pure Pt and Ru particles crystallize in the sam e structure as in the bulk, i.e., face centered cubic (fcc) for platinum an d hexagonal close packed (hcp) for ruthenium. A modification of the cell pa rameters due to size reduction is observed. In particular, evidence is give n for the change of the c/a ratio in Ru particles. The alloy particles are also crystalline, whatever the composition. The role of the composition in the structural transition from the fee structure to the hcp one in nanoscal ed particles is demonstrated. The mechanism of structural transition is ful ly described.