Electronic structure of Fe-bearing lazulites

Grodzicki, M., Redhammer, G. J., Amthauer, G., Schunemann, V., Trautwein, A., Velickov, B. and Schmid-Beurmann, P. (2003) Electronic structure of Fe-bearing lazulites American Mineralogist, 88 (4). pp. 481-488.

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The Fe end-members scorzalite [Fe2+Al23+(PO4)(2)(OH)(2)] and barbosalite [Fe2+Fe23+(PO4)(2)(OH)(2)] of the lazulite series have been investigated by Mossbauer and diffuse reflectance spectroscopy, and by electronic structure calculations in the local spin density approximation. The measured quadrupole splitting (DeltaE(Q) = -3.99 mm/s) in scorzalite is in quantitative agreement with the calculated value (DeltaE(Q) = -3.90 mm/s), as well as its temperature dependence. The optical spectrum of barbosalite can be resolved into three peaks at 8985 cm(-1), 10980 cm(-1), and 14110 cm-1. These positions correlate well with the two calculated spin-allowed d-d transitions at 8824 cm-1 and 11477 cm-1, and with an intervalence charge transfer transition at about 14200 cm-1. The calculated low-temperature magnetic structure of barbosalite is characterized by a strong antiferromagnetic coupling (J = -84.6 cm-1) within the octahedral Fe3+-chains, whereas a weak antiferromagnetic coupling within the trioctabedral subunit cannot be considered as conclusive. The analysis of the charge and spin densities reveals that more than 90% of the covalent part of the iron-ligand bonds arises from the Fe(4s,4p)-electrons. Clusters of at least 95 atoms are required to reproduce the available experimental data with quantitative accuracy.

Document Type: Article
Keywords: molecular-orbital calculations isomer-shifts mossbauer-spectroscopy calibration fe-57 iron barbosalite clusters valence ligand
Research affiliation: Kiel University
ISSN: 0003-004X
Date Deposited: 24 Jan 2012 05:43
Last Modified: 08 Oct 2012 10:35
URI: http://eprints.uni-kiel.de/id/eprint/16190

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