Deviation from Matthiessen's rule in electron-irradiated copper

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Abstract
Deviations from Matthiessen's rule (which states that the electrical-resistivity contributions of two different types of scatterers in a metal are additive) occur generally. This paper concerns itself with the deviations arising from relatively simple scatterers: by point defects (vacancies and interstitials) created by electron irradiation and by phonons. Flexibility in the control of point-defect concentration is the major experimental feature of the work. Deviations from Matthiessen's rule in pure copper were studied over as wide a temperature range as possible, commensurate with the irradiation and annealing schedule used. In particular, the deviations were studied as effected by recovery in the first three major defect annealing stages. When analyzing effects due to stage-I annealing, damage was produced by irradiation at 4°K; in stages II and III, damage was produced at 4 and at 80°K. In all cases, the electron energy was 1.5 MeV. The deviations were analyzed by considering two deviation-producing mechanisms: the "two-band" model and changes in the temperature-dependent part of the electrical resistivity. At low temperatures (below 35°K) the two-band form explains the data when separate temperature dependences for scattering of neck and belly electrons are taken into account. Contributions due to changes in the temperature-dependent part of the electrical resisitivity appeared to play no substantial part. In the stage-II region the deviations arising from irradiation at 4°K and irradiation at 80°K were of a similar form, indicating that the nature of the irradiation-induced scatterers in both cases were essentially the same. This may be explained by showing that the interstitials in either case existed as clusters—in the 80°K case, nucleated on impurity traps and, in the 4°K case, self-nucleated. In the stage-III region, contributions to the deviation from changes in the temperature-dependent part of the electrical resisitivity were quite large. Similarities between the deviations here and those arising in the neutron-irradiated copper without stage-III annealing give support to the model that the mobile defect in stage III is the vacancy.