Defect annealing studies on metals by positron annihilation and electrical resitivity measurements

Abstract

Doppler-broadening positron-annihilation measurements combined with electrical-resistivity measurements were performed on Cu and Al samples, irradiated by high-energy electrons at liquid-helium temperature. A defect-specific parameter $R$ was determined from the shape of the 511-keV annihilation line. The $R$ parameter is found to be independent of the defect concentration $C$ and the positron trapping constant $\ensuremath{\mu}$ within the framework of the two-state trapping model. During isochronal annealing of electron-irradiated copper the line-shape parameter $\ensuremath{\Delta}{I}_{v}$ increases in stage III, whereas the electrical resistivity decreases, indicating a reduction in the Frenkel-defect concentration. These two combined effects and the pronounced steps in the $R$ parameter during stage-III annealing, which are found to be dose independent, signify that radiation-produced vacancies become mobile and coalesce into clusters before they anneal out. The positron trapping constant $\ensuremath{\mu}$ for vacancies in Cu was determined to be $\ensuremath{\mu}=(4.25\ifmmode\times\else\texttimes\fi{}0.8)\ifmmode\times\else\texttimes\fi{}{10}^{14}$ ${\mathrm{sec}}^{\ensuremath{-}1}$. Furthermore, the annealing behavior of copper and aluminum samples, deformed plastically at 77 K and irradiated at 4.2 K by electrons, respectively, is discussed. In both cases no indication for the formation of vacancy agglomerates is found during annealing. The $R$-parameter analysis is also applied to the data for electron-irradiated Mo, as reported by Eldrup et al.