Abstract
The dependence of the electronic and the crystallographic structure on temperature of synthetic Mnbearing ilvaites CaFe2+ 2-xMn2+ xFe3+ [Si2O7/O/OH] with 0≤x≤0.19 has been investigated. The change of the electronic structure was studied by 57Fe Mössbauer spectroscopy. The spectra show an increasing valence fluctuation rate between Fe2+ and Fe3+ in the double chain of edge-sharing octahedra with increasing temperature resulting in a mixed valent state of iron. The valence fluctuation rate is distinctly increased by the Mnsubstitution. The temperature of the crystallographic phase transition T x as studied by a high temperature Guinier method is distinctly lowered by the Mn-substitution (x = 0.0, T x=390K; x = 0.12, T x =370K; x = 0.19, T x=295K). The reasons for this behaviour are discussed in terms of Fe2 +, Fe3 + cation order-disorder, electronic relaxation rate, and relaxation of the lattice. In the monoclinic phase there is electron hopping between Fe2 +, Fe3 + pairs whereas in the orthorhombic phase there is extended electron delocalization via a narrow, d-band mechanism.
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Ghazi-Bayat, B., Behruzi, M., Litterst, F.J. et al. Crystallographic phase transition and valence fluctuation in synthetic mn-bearing ilvaite CaFe2+ 2-x Mn2+ xFe3+ [Si2O7/O/(OH)]. Phys Chem Minerals 18, 491–496 (1992). https://doi.org/10.1007/BF00205263
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DOI: https://doi.org/10.1007/BF00205263