Resonant X-ray diffraction and differential atomic pair distribution functions method is illustrated with results from a study of 4.5(3) nm Pt, Au and Pt0.51Au0.49 particles. By doing experiments at two energies close to the K absorption edge of Pt the atomic correlations relative to Pt and Au atoms in the alloy particles are differentiated. The experimental data show that Pt and Au atoms in all three samples arrange in a face centered cubic type structure while keeping their bond lengths of 2.76 Å and 2.86 Å, respectively, virtually unchanged. This leads to increased local structural distortions in the alloyed Pt0.51Au0.49 particles that may affect their catalitic properties substantially.
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