Properties of iron impurity in aluminium matrix studied by Mössbauer spectroscopy

Abstract

An aluminium based alloy containing 240 p.p.m. of ⁵⁷Fe in substitution was studied by the Mössbauer effect. The change in the spectrum was followed as a function both of the observation temperature and of the thermal story of the specimen. The overall variation of the fraction due to the recoil-less effect (coefficient f) and of the second order Döppler shift gave the same value of about 0.75 for the ratio λ'/λ of the force constants around the impurity and in the matrix. An anharmonic behaviour of the coefficient f for temperatures equal to or higher than the ambient temperature was observed. A linear variation of the isomer shift shows the regular increase of the electronic density on the Fe nuclei. A change in the Mössbauer peak widths, as well as the discontinuity in the curve of the peak positions as a function of temperature near 330 K for a just-quenched alloy, allows one to follow the vacancy agglomeration process, the formation and the annealing of dislocation loops up to the initial stages of the precipitation of Fe.