The effects of covalency on Mossbauer hyperfine interactions in RbFeS2

Using point charge model calculations, constrained by the Mossbauer nuclear resonance data, the charge distribution and the 4s electron density at the Fe57 nucleus in RbFeS2 is determined. These values are compared with estimates obtained using Danon's reinterpretation of the Walker, Wertheim and Jaccarino Isomer Shift calibration (Modified WWJ Plot). The low temperature Mossbauer spectroscopic data exhibits the appearance of a magnetic hyperfine interaction at about -880 C. The measured hyperfine parameters in this compound are compared with that observed for KFeS2 by considering the relative FE-S covalent character, the related X-Ray structure parameters and cationic radius