Mössbauer Effect in Dilute Alloys of Iron in Aluminum

The Mössbauer spectrum of dilute alloys of ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ in aluminum has been studied. In the concentration range from 0. 005 to 1.2-at.% Fe, the spectrum consists partly of a single-line component due to Fe in solid solution in aluminum metal and partly of a multiple-line component associated with Fe in ${\mathrm{Fe}}_4$ ${\mathrm{Al}}_{13}$. These two components can be distinguished from each other by the differences in their behavior when either concentration or temperature is varied. In the course of this investigation we achieved some understanding of two peculiar observations that had led us to undertake this study. (i) Bara et al. had obtained a succession of unusual spectra for excited ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ nuclei formed by the decay of ${}_{}{}^{57}{}_{}{}^{}\mathrm{Co}$ which had been diffused into aluminum metal. We can explain their results on the assumption that the ${}_{}{}^{57}{}_{}{}^{}\mathrm{Co}$ first went into solid solution in the aluminum, was then converted to metallic cobalt during further heat treatments, and finally became oxidized. (ii) From recoil-implanted ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ in aluminum, Sprouse et al. had obtained a Mössbauer spectrum that appeared to consist of two poorly resolved broad lines instead of the expected single sharp line. We believe this modification of the spectrum must be attributed to radiation damage produced by the implantation of the ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ atoms. In the vicinity of the final position of each implanted atom this damage is probably in the form of lattice vacancies.