electronic structure and properties of equi-atomic CuAu

The electronic structure of equi-atomic CuAu has been investigated by a combination of photoelectron spectroscopy and first-principles band structure calculations. The study includes the first ever ARUPS and ARAES measurements from a single crystal of CuAu I. We have studied in detail the energy dispersion and shifts of a Tamm state on the (001) and (100) surfaces and we determined the surface lattice constants and the dependencies of the energy shifts on atomic concentration and geometry. Two new surface states were found on the two surfaces and their properties have been investigated. Comparisons between the valence band spectra from the two samples of CuAu I have been carried out and the results show that the different atomic arrangements in the crystal do not have a significant effect on the band structure. We also compared spectra from the alloy with those from the parent metals. A series of calculations of the electronic structure of CuAu I has been carried out by the SCF-LMTO-ASA and RKKR methods. We found that the superzone boundaries that are created when the CuAu II phase is formed destroy appreciable regions of Fermi surface, thus, favoring the latter phase. The positions of the new boundaries are related directly to the period of the long period superlattice and we have investigated their dependence on the e/a ratio and pressure. The results are in very good agreement with previous experimental measurements. We also calculated the Fermi surfaces of three disordered Cu-Au alloys near the equi-atomic composition using the KKR-CPA scheme. The results have shown strong evidence that the Fermi surface topology may play an important role in stabilizing and determining the modulation of the LPS in CuAu II.