Properties of iron impurity in aluminium matrix studied by Mössbauer spectroscopy

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.