Specific heat below 3 °K of copper–gold alloys

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Abstract
Specific heat measurements were made between 0.4 and 3.0 °K on the disordered and two ordered phases of the equiatomic alloy CuAu, and also on CuAu3 in the disordered and partially ordered condition. The two samples of the disordered equiatomic alloy measured were found to be unstable, the specific heat on successive measurements slowly changing towards the values obtained for the ordered phase CuAu II. This is a remarkable result because all previous work has shown that the ordered phase formed below 385 °C is CuAu I. The first sample of CuAu I measured showed a distinct 'bump', with the maximum at about 0.7 °K, superimposed on the normal specific heat. A second sample did not show this 'bump' but the specific heat remained slightly anomalous. The nuclear specific heats of the ordered phases CuAu I and CuAu II and the partially ordered CuAu3 are higher than those of the respective disordered phases, supporting the hypothesis that the nuclear term is a quadrupole effect. Taking the present results in conjunction with those of Martin on Cu3Au, it is found that the electronic specific heats of the disordered alloys are fitted reasonably well by Stern's 'charging' theory. Ordering reduces the electronic specific heat by a few percent except for CuAu I where it is increased. The low-temperature limiting Debye temperature is increased by a few percent on ordering except for CuAu I where it is decreased. The Debye temperature changes are consistent with room-temperature Young's modulus measurements on copper–gold alloys. Otherwise it will be noted that the behavior of CuAu I is rather singular.

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