Deviation from Matthiessen's rule at high temperatures: Cu, Ag and Ge in Al

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Abstract
The electrical resistance of Al containing Cu, Ag and Ge has been measured for impurity concentrations from about 0.002 to 0.2 at.%, and at temperatures 723-905K, 293K and 4.2K. An experimental technique is employed in which the impurity material is vacuum deposited onto a pure Al foil at high temperatures, and the resistance increment during the subsequent diffusion process is measured. The method allows accurate determination of impurity resistivity at high temperatures by eliminating possible errors due to difference in size factors between pure and alloyed specimens. Results show that, above room temperature, the ratio of the impurity resistivity to the residual resistivity tends to decrease with increasing temperature and impurity concentration. A general feature of the deviation from Matthiessen's rule is established for these impurities in Al by combining the present high-temperature data with low-temperature ones reported by other investigators.