Mössbauer spectroscopy and molecular orbital calculations on iron bearing omphacite

摘要

A natural iron bearing omphacite with composition Ca0.49 Na0.525 Mg0.424 Al0.43 Fe 0.076 2+ Fe 0.056 3+ Ti0.0024 Mn0.005 Si1.989 O6 from Syros, Greece, has been investigated by Mössbauer spectroscopy. The interpretation of the spectra is based on electronic structure calculations in the local spin density approximation. The calculations emphasize that large clusters, extending beyond the second coordination sphere of iron, are necessary for a reliable description. As suggested by the electronic structure calculations, different environments around the Fe2+ octahedra give rise to slightly different hyperfine parameters, especially affecting the quadrupole splitting. Hence, the measured spectrum has been evaluated based on quadrupole splitting distribution. The calculated values including the temperature dependence are in almost quantitative agreement with the experimentally derived values.