Mössbauer Spectrum of Fe2+ in a Square-Planar Environment

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Abstract
The Mössbauer spectrum of high‐spin Fe2+, square planar coordinated by oxygens in BaFeSi4O10, has been studied in the temperature range 80°—650°K. The spectrum, a quadrupole doublet, was analyzed by computer fitting, and the results statistically tested using the concept of internal and external consistency. Quadrupole splitting and center shift data are reported for the whole range 80°—650°K, and the widths and relative intensities of the lines have been measured at 80° and 295°K. The quadrupole splitting has been successfully correlated with the magnetic susceptibility and electronic spectrum of Fe2+ in BaFeSi4O10. The lattice contribution is found to be slightly larger in magnitude than the valence contribution, and of opposite sign. By studying both randomized and oriented samples the sign of the quadrupole splitting has been determined experimentally, and the anisotropy of the recoil‐free fraction measured. The temperature variation of the center shift has been analyzed in terms of the second‐order Doppler shift, and information on the vibrational motion of the iron atom obtained. The theoretical basis of the method used for analyzing the second‐order Doppler‐shift data is briefly discussed. A correlation between center shift values and coordination number for minerals containing high‐spin ferrous iron is noted; and interesting observations concerning the linewidths, and the effects of heat treatment on the Mössbauer spectrum of gillespite, are reported.