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Mössbauer and IR analysis of iron sites in four ferruginous smectites

¹ School of Physics, Monash University, Victoria 3800, Australia, and ² Department of Civil Engineering, Monash University, Victoria 3800, Australia

^* E-mail: john.cashion{at}sci.monash.edu.au

(Received 26 March 2007; revised 17 October 2007)

⁵⁷Fe Mössbauer spectra of the Na⁺- and Ca²⁺-saturated forms of four ferruginous smectites, displaying a range of compositions, have been fitted with Voigtian profiles to represent (principally) two correlated distributions of isomer shifts and quadrupole splittings for the Fe³⁺ sites. Correlating the areas and hyperfine parameters of these distributions with simulations of the octahedral array of cations based on chemical analyses and infrared spectroscopy has enabled identification of the Fe³⁺ ions that contribute to the outer quadrupole doublet. The octahedral Fe³⁺ sites are characterized as having at least one Mg²⁺ nearest-cation neighbour and probably a cis-configuration with respect to the OH^– ions.

KEYWORDS: Mössbauer spectroscopy, IR, ferruginous, smectites, Voigtian profiles, Fe³⁺, Fe²⁺