Pd-Ti bimetallics: A study of the electronic structure using x-ray photoelectron spectroscopy and x-ray-absorption near-edge structure.

Abstract

We studied the core-level binding-energy shifts and the valence-band behavior of ${\mathrm{Pd}}_{3}$Ti and ${\mathrm{PdTi}}_{2}$ alloys using x-ray photoelectron spectroscopy (XPS) and x-ray-absorption near-edge structure (XANES). The observed Pd core-level shifts in the alloys, relative to the pure metal, were not consistent with the electronegativity predictions. It is proposed that upon alloying there is an increase in the number of sp-like conduction electrons and a decrease in the number of d electrons at the Pd site. This electron redistribution at the noble-metal site in the alloy results in a small net charge flow between Pd and Ti, in the direction in accord with electronegativity predictions. Pd ${\mathit{L}}_{3}$-edge and Ti K-edge XANES provide further evidence of electron redistribution upon alloying. Net charge transfer at the Pd site of ${\mathrm{PdTi}}_{2}$ has been estimated to be 0.29\ifmmode\pm\else\textpm\fi{}0.02 electron counts on the basis of a charge compensation model, results from XPS binding-energy shift, and XANES white-line areas. The observed Pd valence-band narrowing and shifts to a higher binding energy are also explained in terms of dilution and charge redistribution.