ELECTRONIC-STRUCTURE OF NI-CU ALLOYS - THE D-ELECTRON CHARGE-DISTRIBUTION

This work investigates charge redistribution in a series of Ni-Cu allo ys using x-ray photoemission spectroscopy (XPS) and Ni/Cu L-3,L-2- and K-edge x-ray-absorption near-edge structure (XANES). XPS results show that the constituent d bands are well separated and shifted to a slig htly higher binding energy upon dilution into the other host, indicati ng that the atomic sites in the alloy are not as well screened relativ e to the pure metal. However, no significant d-band narrowing is obser ved, suggesting that there is modest d-d interaction in the alloys. In contrast to the XPS observation, XANES results show a reduction in wh ite-line intensity at both edges relative to the pure metal suggesting that both Ni and Cu sites gain d charge. The unoccupied Ni d band is far from fully occupied even at infinite dilution. The discrepancy bet ween the implications of the XPS and XANES results is dealt with using a charge redistribution model in which s-p-d rehybridization takes pl ace at both sites within the framework of electroneutrality and electr onegativity considerations. It appears that both Ni and Cu gain a smal l but measurable amount of d charge in alloy formation through rehybri dization (loss of non-d conduction charge). Possible connection betwee n these results and the disappearance of ferromagnetism in Ni1-xCux al loys at x>0.6 is discussed.