A mössbauer study in the troilite-pyrrhotite system

Abstract

SUMMARY In this thesis, several compounds in the iron monosulfide system ranging in composition from troilite (FeS) to pyrrhotite (Fe7S8) -have been studied. Emphasis has been placed on the temperature dependence of the characteristics measured by the Mössbauer effect. In troilite, the crystallographic phase transition near 400 0 K was of special interest. In pyrrhotite; the distribution of vacancies and the ordering of ferrous and ferric ions was examined. The investigation has included the development of an improved method for preparation of samples, which minimizes oxygen impurity. In the region of nearly stoichiometric FeS, we have proven conclusively that the Morin transition is only associated with the R3m phase, it is noted that the Néel en Morin transitions must be accompanied by changes in magnetic space group. The probable existence of iron-rich FeS, with interstitial iron, has been made plausible. Interstitials in sulfur-rich FeS have not been observed. The spin directions in both the R3m and P62c phases have been deduced from the combined quadrupole and magnetic hyperfine splittings, possible disagreement with previously assumed directions has been pointed out. Further the orbital ground state of the ferrous ions in their crystalline surroundings has been determined from the temperature dependence and of the quadrupole splitting and the calculated lattice contribution to the electric field gradient tensor...