Lattice location of xenon impurities implanted in iron derived from mössbauer effect measurements

Abstract

Abstract Mössbauer effect measurements were performed with sources of 133Xe implanted in polycrystalline iron at temperatures from 90 K to 480 K, using the 81 keV transition in 133Cs, in order to obtain information about the lattice sites of the implanted impurities. Annealing experiments were done with sources implanted at 90 K and at room temperature. The Mössbauer spectra were analyzed on the basis of an earlier model, assuming three spectral components (h, i, r) with high, intermediate and low hyperfine fields and recoilless fractions, respectively. A careful analysis of the absorption depths of the three components suggested, however, that the l-component can be divided in two parts: one, consisting of xenon atoms associated with a few vacancies (typically from 2 to S), is again called the l-component, while the second part, consisting of xenon atoms in rather large vacancy clusters (say, 5 or more vacancies), has a very small recoilless fraction and therefore hardly contributes to the Mössbauer absorption. The latter part is called the z-component. Its existence is directly concluded from the abnormal increase with implantation or annealing temperature of the l-component. This increase is much stronger than the decrease (if present) of the h-and i-components. The l-sites are thought to be the most stable Xe-sites at temperatures below 600 K; the increase of the l-component is mainly caused by a decrease of the z-component, due to break up of large Xe-vacancy clusters. Values of the site populations are given in terms of this four-component model. The recoilless fractions of the three visible components in the Mössbauer spectra, measured by varying the source temperature, are in agreement with previous results. To study the influence of the implanted dose, a large fraction of the activity of one source, implanted at room temperature, was removed by etching. Only a slight increase in the substitutional fraction was observed. From a re-analysis of measurements on sources obtained at different implantation energies the influence of this energy on the site populations is established.