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Three Oxidation States of Manganese in the Barium Hexaferrite BaFe12-xMnxO19

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Hu,  Zhiwei
Zhiwei Hu, Physics of Correlated Matter, Max Planck Institute for Chemical Physics of Solids, Max Planck Society;

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Valldor,  Martin
Martin Valldor, Physics of Correlated Matter, Max Planck Institute for Chemical Physics of Solids, Max Planck Society;

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Kuo,  Chang-Yang
Physics of Correlated Matter, Max Planck Institute for Chemical Physics of Solids, Max Planck Society;

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Tjeng,  Liu Hao
Liu Hao Tjeng, Physics of Correlated Matter, Max Planck Institute for Chemical Physics of Solids, Max Planck Society;

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Citation

Nemrava, S., Vinnik, D. A., Hu, Z., Valldor, M., Kuo, C.-Y., Zherebtsov, D. A., et al. (2017). Three Oxidation States of Manganese in the Barium Hexaferrite BaFe12-xMnxO19. Inorganic Chemistry, 56(7), 3861-3866. doi:10.1021/acs.inorgchem.6b02688.


Cite as: http://hdl.handle.net/11858/00-001M-0000-002D-3F8B-3
Abstract
The coexistence of three valence states of Mn ions, namely, +2, +3, and +4, in substituted magnetoplumbite-type BaFe12xMnxO19 was observed by soft X-ray absorption spectroscopy at the Mn-L-2,L-3 edge. We infer that the occurrence of multiple valence states of Mn situated in the pristine purely iron(III) compound BaFe12O19 is made possible by the fact that the charge disproportionation of Mn3+ into Mn2+ and Mn4+ requires less energy than that of Fe3+ into Fe2+ and Fe4+, related to the smaller effective Coulomb interaction of Mn3+ (d(4)) compared to Fe3+ (d(5)). The different chemical environments determine the location of the differently charged ions: with Mn3+ occupying positions with (distorted) octahedral local symmetry, Mn4+ ions prefer octahedrally coordinated sites in order to optimize their covalent bonding. Larger and more ionic bonded Mn2+ ions with a spherical charge distribution accumulate at tetrahedrally coordinated sites. Simulations of the experimental Mn-L-2,L-3 XAS spectra of two different samples with x = 1.5 and x = 1.7 led to Mn2+:Mn3+:Mn4+ atomic ratios of 0.16:0.51:0.33 and 0.19:0.57:0.24.