Densities of States of Paramagnetic Cu-Ni Alloys

The densities of states of the near ideally substitutional random-alloy system Cu-Ni are calculated using the coherent-potential approximation for a range of concentrations of the constituents across the complete alloy diagram. It is shown that previous model calculations for Ni-rich paramagnetic Cu-Ni alloys using the coherent-potential approximation can be extended to alloys of arbitrary concentration if appropriate Cu and Ni potential functions are used. The results obtained are consistent with experimental photoemission and soft-x-ray emission profiles in so far as comparisons can be effected. The results indicate the limits of this simple nonmagnetic random-alloy theory for discussing the conventional low-temperature specific-heat data of these alloys. For Cu-rich alloys the results correspond to a split-band regime while for Ni-rich alloys the $d$ bands associated with Cu and with Ni sites in the alloy overlap to a considerable extent. For all Cu-Ni alloys the rigid-band model and the virtual-crystal approximation are quite inappropriate.