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.

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

Electronic structure of metallic glasses

A theory of angle-resolved photoemission from the surface of a random alloy is described. It is argued that this theory contains a proper treatment of the disorder (via the Korringa-Kohn-Rostoker coherent potential approximation, KKR CPA), the surface, the LEED-type final state, and the electron-photon matrix elements. The results are illustrated by comparing calculations for pure Cu and Cu-Ni alloys.

Theory of photoemission from random alloys

We present self-consistent-field Korringa-Kohn-Rostoker coherent-potential-approximation calculations of the electronic density of states of random ${\mathrm{Cu}}_{\mathrm{c}}$${\mathrm{Pd}}_{1\mathrm{\ensuremath{-}}\mathrm{c}}$ alloys. We find strong hybridization of the palladium d bands with the copper d bands over the entire concentration range. We do not obtain a palladium virtual bound state for the copper-rich alloys and therefore contradict the interpretation generally placed on valence-band x-ray photoelectron spectroscopy (XPS) spectra for Cu-Pd. Nevertheless, our first-principles calculations of the XPS spectra are in excellent agreement with recent measurements, and we discuss why this is so. Furthermore, we compare our density of states at the Fermi energy with specific-heat measurements.

Electronic density of states and the x-ray photoelectron spectra of the valence band of Cu-Pd alloys.

Multiple scattering theory is used to obtain a local, one-electron approximation for calculating the valence-band XPS spectra of solids and the generalisation to random substitutional alloys is described The nature of the final state and the influence of matrix elements on the shape of the spectra are discussed The local approximation is shown to be rather accurate at high photon energies The authors present calculations (based on the KKR CPA) for AgxPd1-x alloys using both self-consistent and non-self-consistent potentials and compare the results with experimental data

https://iopscience.iop.org/article/10.1088/0305-4608/14/4/025/pdf

Theory of valence-band XPS spectra of random alloys: application to AgxPd1-x

Calculations of the L alpha soft X-ray emission spectra of Cu-Ni alloys using the muffin-tin form of the coherent potential approximation (KKR-CPA) are presented. The transition matrix elements are determined exactly within the KKR-CPA, and lifetime broadening is included. The results of new experiments on the L alpha spectra are also reported and combined with X-ray photoemission measurements of the core state binding energies, so that the relative positions of the Cu and Ni emission bands may be determined. Good agreement between theory and experiment is found, confirming the KKR-CPA description of the local densities of states in Cu-Ni alloys. Striking non rigid-band behaviour is observed. It is suggested that soft X-ray studies of the type the authors describe should be a useful probe of alloy potential functions.

Soft X-ray emission and the local densities of states in Cu-Ni alloys

The X-ray emission spectra of Pd and Zr in glassy Pd30Zr70 have been measured and are compared with the emissions from pure polycrystalline Pd and Zr samples. The local contributions to the total density of states are obtained from the alloy measurements and located with respect to the Fermi level by means of core-level binding energy determinations. The interesting alloying effects are analysed and discussed in relation to a new cluster approximation and previous photoemission measurements.

The local densities of states in glassy Pd30Zr70 (X-ray emission spectra)

The local densities of states of TLxZr1-x(x approximately 0.3) metallic glasses, where TL is Co, Ni, Rh or Pd, have been investigated by soft X-ray emission spectroscopy. Unlike the local Rh and Pd 4d states which overlap the part of the Zr 4d band with high binding energy, the Co and Ni 3d states are centred on the Zr 4d states. The contribution to the density of states at the Fermi level from the TL elements is more pronounced for the 3d than for the 4d elements. The results are discussed in relation to density of states calculations on disordered and ordered alloys. Particularly good agreement is obtained with density of states calculations performed for ordered structures, indicating the dominant effect of chemical short-range order.

C F Hague

Papers

Soft X-ray emission and the local densities of states in Cu-Ni alloys

The local densities of states in glassy Pd30Zr70 (X-ray emission spectra)

Local densities of states of Zr-based transition metal glasses