PARTIAL SPECTRAL WEIGHTS OF DISORDERED CU-AU ALLOYS

We present valence band photoemission spectra of polycrystalline CuxAu 1-x (x = 0.10, 0.25, 0.50, 0.75, 0.90) disordered binary alloys taken with variable incident-photon energies using synchrotron radiation. Ta king advantage of the Cooper minimum phenomenon of the Au 5d band and taking proper account of the photoionization matrix element, we obtain experimental partial spectral weights for the alloys determined from the measured ratio of Au 5d and Cu 3d photoionization cross sections. We find that the Au partial density of states in dilute Au alloys is v ery strongly hybridized with the Cu host band and its bandwidth is not much reduced, contrary to the conclusion of some earlier work which c laimed that the Au states have a greatly narrowed bandwidth due to the band repulsion between different d bands. Our finding is consistent w ith recent theoretical results. The lattice relaxation effect on the e lectronic structures of Cu-Au alloys is also investigated using ultrav iolet photoemission spectroscopy. Compared with the bandwidths of orde red alloys which do not suffer lattice relaxation, those of disordered alloys are reduced by a small amount, which can be interpreted as the result of both the total volume change and the lattice relaxation eff ects, whose magnitudes are comparable.