Electronic specific heats of copper-based alloys

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Abstract
The experimental behaviour of the electronic specific heat coefficient γ of face-centred cubic disordered Cu-Zn alloys, which shows positive initial slopes against zinc concentrations, is explained by taking into account the level broadening of the d band which results from the presence of impurity potentials. As a result of level broadening, the d band has the effect of increasing the density of states at the Fermi level of an alloy. This contribution increases as zinc concentrations are increased, while the contribution from the s band is in the opposite direction. The density of states of the d band calculated by Burdick is used, and that of the s band is calculated by use of the nearly free-electron approximation by Ziman. The position of the d band relative to the Fermi level in an alloy is determined from the absorption edge of Cu-Zn which has been measured by Biondi and Rayne. Then only one unknown parameter, which represents the level breadth of the d state, appears in the expression for γ. It is shown that when the value of this parameter is chosen appropriately the present theory agrees fairly well with experiment. The experimental data for γ in face-centred cubic disordered Cu1-2xZnxNix, which increases with x, can be explained using the values of the level breadth parameter found from analysis of Cu-Zn and Cu-Ni. This fact shows that the behaviour of γ for copper-based alloys can be interpreted consistently on the basis of the present model.