Determination of the electric field gradient tensor in ferrous chloride tetrahydrate using a polarized mössbauer source

The orientation of the electric field gradient tensor at the iron nucleus in a single crystal of FeCl₂·4H₂O has been determined using a polarized Mössbauer source of ⁵⁷Co in iron metal. The data analysis embodied an accurate thickness correction for the polarization of the absorption cross-section. The principal axis of the tensor lies close to the FeCl bonds of the trans-octahedral FeCl₂(H₂O)₄ unit, but the minor axes are directed between the FeO bonds. The value of the asymmetry parameter obtained, n = 0.40 ± 0.15, is significantly larger than previous estimates.