Electronic structure of disordered Au-Pd alloys studied by electron spectroscopies

Abstract

The occupied and unoccupied electronic structures of disordered AuxPd1-x alloys are studied by valence band photoemission, bremsstrahlung isochromat spectroscopy (BIS), and x-ray absorption near-edge spectroscopy (XANES). The occupied partial spectral weights (PSW's) of Au 5d and Pd 4d states are obtained from the valence-band photoemission spectra using synchrotron radiation by taking the matrix-element effect into account. We use the Cooper minimum phenomenon of the Pd 4d states with the measured ratios of photoionization cross sections. The Pd 4d. PSW's are found to form a Virtual bound state in the Pd-diluted alloy but become broader as the Pd concentration increases due to the Pd 4d-Pd 4d hybridization. On the other hand, Au 5d(5/2) States show the common-band behavior due to the appreciable mixing with Pd 4d(5/2) states, while Au 5d(3/2) states retain their sharp structure and show the split-band behavior. These experimental PSW's of Au-Pd alloys are in good qualitative agreement with the results of recent self-consistent-held coherent-potential-approximation calculations. The comparison of the experimental Pd PSW of Au-Pd with those of other Pd-noble-metal alloys clearly shows that in noble-metal-rich alloys, the mixing of Pd 4d states with host d bands increases in the order of Ag-Pd, Au-Pd, Cu-Pd systems. This trend results in the split-band for Au-Pd and Ag-Pd in Pd diluted alloys, but gives the common band for Cu-Pd. The unoccupied Pd 4d states of disordered AuxPd1-x alloys obtained from BIS and XANES spectra show the gradual filling of Pd 4d states as the Au concentration is increased, but it is not completely filled even in the Pd-diluted alloy. [S0163-1829(98)00339-7].