Studies of defects at thermal equilibrium and melting in Cu and Ni by positron annihilation

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Abstract
Peak counting rates in the angular correlation were measured as a function of temperature above room temperature in the solid and liquid phases of Cu and in the solid phase of Ni. The peak counting rates in Cu increased about 17% upon melting. Temperature dependence of the peak counting rates in the liquid phase shows a hump at 1150 degrees C. Two possible explanations were proposed for this anomaly. The data in the solid phases were numerically analysed by the trapping model in which it was assumed that only single vacancies and divacancies are effective. The data at lower temperatures, where the effect of divacancies is sufficiently small, were analysed by the conventional trapping model of single vacancies. The results of both analyses are consistent. The characteristic temperature Tc in the trapping model was defined. It was demonstrated that Tc is proportional to E1VF. The experimental values of Tc were plotted against E1VF for various FCC metals and linear relationship between E1VF and Tc was also experimentally found.