Mössbauer 57Fe isomer shift as a measure of valence in mixed-valence iron sulfides

Abstract

An empirical formula relating the room-temperature isomer shift δ for high-spin iron in sulfur coordination to the effective iron valence 〈m +〉, of the form δ = A - B 〈m +〉, has been refined for tetrahedral coordination and modified by an inclusion of orbital degeneracy into the definition of 〈m+〉; it has also been extended to include octahedral coordination by adding 0.17 mm/sec to A. For a given 〈m+〉, the I.S. is shown to be sensitive to nearest-neighbor anion coordination, but much less sensitive than the hyperfine field to the competitive bonding with these anions. However, the sign of the deviation from the empirical line indicates the direction of any net superexchange charge transfer to or from the iron atom. The utility of the relationship is illustrated by application to a wide range of problems. © 1982.