Local structure around Fe in Mg0.9Fe0.1SiO3 perovskite: An X-ray absorption spectroscopy study at Fe-K edge
Faroes, François; Guyot, François; Andrault, Denis; Wang, Yanbin
European Journal of Mineralogy Volume 6 Number 3 (1994), p. 303 - 312
published: Jun 7, 1994
manuscript accepted: Jan 11, 1994
manuscript received: Aug 16, 1993
ArtNo. ESP147050603001, Price: 29.00 €
Abstract A polycrystalline Mg0.9Fe0.1SiOperovskite, synthesized at 260 kbar and 1973 K in a multi-anvil apparatus, and the enstatite starting material have been probed by X-ray absorption fine structure (XAFS) spectroscopy at the Fe K-edge under ambient conditions. XAFS analysis of the local structure around Fe in perovskite shows evidence for (1) the presence of major amounts of divalent iron, (2) a higher average Fe-O distance in perovskite compared with enstatite, and (3) a wide distribution of the individual Fe-O distances, suggesting that a simple harmonic model to fit XAFS data may not be appropriate. Although a classic Gaussian model of the O-environment is consistent with the presence of 6xFe2+-O correlations at 2.16(2) Å, a doubleharmonic (e.g., 2 x Gaussian) fit reveals the presence of 2.8 ±0.5 additional Fe-O first-neighbours correlations at a mean Fe-O distance of -2.30(2) Å, yielding 8.4 ± 1 Fe-O first-neighbours correlations around Fe with a mean Fe-O distance of 2.23 (3) Å. An anharmonic fit (cumulant expansion method) leads to a similar conclusion. These data compare favourably with those for the Mg-site in the same perovskite (8xMg-O at 2.20 Å), suggesting that Fe substitutes preferentially for Mg in the perovskite sample.