Characterization of Copper Palladium Oxide Solid Solutions by X‑ray Diffraction, X‑ray Photoelectron Spectroscopy, and Auger Electron Spectroscopy

• Published in: Journal of physical chemistry. C Vol. 117; no. 14; pp. 7039 - 7049
• Main Authors: Christensen, Gregory L, Langell, Marjorie A
• Format: Journal Article
• Language: English
• Published: Columbus, OH American Chemical Society 11-04-2013
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Electron and ion emission by liquids and solids; impact phenomena; Exact sciences and technology; Inorganic compounds; Photoemission and photoelectron spectra; Physics; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Tetragonal lattices; Phase transformations; Vegard law; XRD; Lattice parameters; AES; Palladium oxide; Solid solutions; Binding energy; Chemical composition; Madelung constant; Copper oxide; X-ray photoelectron spectra; Crystal structure
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp310344r

Copper palladium oxide, Cu x Pd1–x O, forms a homogeneous solid solution over the wide range of 0 ≤ x ≤ 0.725 in which compositional variation can be correlated with structural and chemical environmental changes. After a small lag at low Cu2+ concentrations, where the lattice cell parameters are pinned to that of the pure PdO structure, Cu x Pd1–x O lattice parameters follow Vegard’s law in which the cell volume decreases linearly with x, indicating a homogeneous solution in which Cu2+ randomly replaces the larger Pd2+ cation. The crystal structure also undergoes an increase in the c/a cell ratio, which relaxes the tetragonal distortion around the metal cation and shifts the metal–oxygen distance toward that of pure CuO (tenorite). X-ray photoelectron spectroscopy (XPS) shows an unusual shift in cation binding energies in which both Pd 3d and Cu 2p linearly increase with increased Cu2+ concentration, a result of the increased Madelung energy and relaxation effects which occur during the photoemission process. XPS and Auger electron spectroscopy (AES) indicate that the surface composition is comparable to that of the bulk, and copper XPS Auger parameter analysis confirms a different, and variable, environment for copper in Cu x Pd1–x O than is found in pure tenorite.