Electronic structure of Ni and Pd alloys. I. X-ray photoelectron spectroscopy of the valence bands

Abstract

X-ray photoelectron (XPS) spectra of the valence bands of approximately 60 Ni and Pd alloys and intermetallic compounds with 20 different elements are presented. In alloys with electropositive elements the Ni and Pd $d$-band centroids move to larger binding energies and the density of $d$ states at the Fermi level (${E}_{F}$) is greatly decreased, indicating that the Ni and Pd $d$ bands are being filled. The Ni and Pd $d$ bands become narrower in alloys with electropositive elements. It is shown that in such alloys, the Ni-$M$ or Pd-$M$ interactions give a significant contribution to the Ni and Pd bandwidths. This contribution is larger when the second element $M$ has a large density of states at the energy of the Ni or Pd $d$ bands in the alloy. As this contribution is small in systems that form complicated structural types and glasses we speculate that its absence helps stabilize such structures. The satellite at \ensuremath{\sim}6 eV in the XPS spectrum of Ni is found to weaken and shifts to higher binding energy in alloys with electropositive metals. In the twelve alloys where its intensity is large enough to allow us to identify its energy, the binding energy of the satellite agrees with the two-electron binding energy of the Ni $^{1}G {d}^{8}$ term derived from Auger spectroscopy. The site- and symmetry-selected densities-of-states curves were calculated for 14 of the alloys to show that this filling is largely due to changes in the hybridization of the Ni or Pd $d$ bands with the partner element bands. The actual transfer of Ni and Pd $d$ electrons is probably small. These observations are used to rationalize published results of specific-heat and magnetic measurements on such alloys.