Impurity Effect on Charge and Spin Density in α-Fe - Comparison between Cellular Model, Ab Initio Calculations and Experiment

Abstract

The influence of the impurity substituted on the regular site in the BCC α-Fe on charge and spin density on the adjacent iron nuclei has been studied by the ab initio method within framework of the full-potential linearized augmented plane-wave formalism applying density functional theorem. Results were correlated with the phenomenological cellular atomic model of Miedema and van der Woude and with the Mössbauer spectroscopy experimental data. PACS: 75.50.Bb, 76.80.+y 1. Introduction Impurity substituted on the regular iron site within BCC α-Fe has influence on the charge (electron) density and electron spin density (hyperfine field) on the adjacent iron nuclei. One can study these effects by means of the 57 Fe Mössbauer spectroscopy. Namely, the average isomer shift (charge density) and hyperfine field varies with the impurity concentration for random distribution of impurities. Additionally, one can see individual effect of impurities to the second and sometimes to the third co-ordination shell. Hence, the impurity has effect on the average isomer shift S , while individual perturbations to the particular impurity could be described as ∆S n with the index n denoting subsequent co-ordination shells around the resonant atom. Corresponding perturbations of the spin density influence the average hyperfine field B and lead to the individual impurity effects ∆B n [1].Parameters described above could be determined from the Mössbauer spectrum. Usually, one has to collect a series of spectra versus impurity concentration c. On the other hand, one can calculate electron density on the iron nucleus for single impurity -the latter located at various co-ordination shells around resonant atom. Similar calculations could be performed for the spin density, i.e., for the hyperfine field.The phenomenological cellular atomic model (CAM) of alloys proposed by Miedema and van der Woude [2,3] could be used to estimate the average isomer shift S M due to impurities, and to estimate contribution to the isomer shift caused by the impurity in the first co-ordination shell ∆S

Transition metal impurity effect on charge and spin density in iron: Ab initio calculations and comparison with Mössbauer data

“…It has been found previously [31] that ab initio calculated perturbations of the electron density 1 ∆S (see Table 2) are in fair agreement with the same perturbations obtained within cellular atomic model of Miedema and van der Woude [32,33]. Recent ab initio studies of the hyperfine fields in the iron alloys with 3d impurities performed by Rahman et al [7] are in good agreement with our results.…”

An Enthalpy of Solution of Silicon in Iron Studied by ^{57}Fe Mössbauer Spectroscopy

“…This fact suggests that influence of Si atoms on 57 Fe nuclei is much more complicated and it cannot be described by simple additive model. Finally, it is worth noting that the obtained values of ∆IS1 are in quite good agreement with ab initio results presented by Błachowski et al [15].…”

Mössbauer spectroscopy evidence of intrinsic non‐stoichiometry in iron telluride single crystals

“…The unconventional lines intensities ratio of the green subspectrum (Fe2 group, see details in Section (Discussion)) needs further investigation. We expect that ab initio calculation can shed light on this peculiarity .…”