Mössbauer study of 57Fe in the pyrite-type dichalcogenides

Abstract

The isomer shift and the quadrupole splitting of 57Fe in the pyrite-type dichalcogenides, FeS2–CoS2–NiS2–NiSe2 and CoSe2, were measured at room temperature. It is concluded that the effects of atomic distance and electronegativity of ligand make comparable contributions to the isomer shift of a divalent iron in low spin state. In high spin state, the contribution of atomic distance is smaller than that of electronegativity. The lattice term of electric field gradient gives a large contribution to the quadrupole splitting. The isomer shift and the quadrupole splitting of Fe1–yCoyS2 change around y=0.5 where the concentration dependence of resistivity changes. In NiS2–xSex, the quadrupole splitting of 57Fe becomes small with increasing x at the metal–semiconductor phase boundary.