Non-stoichiometry and local order in minerals with the rockbridgeite structure

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Marco E. Ciriotti
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Non-stoichiometry and local order in minerals with the rockbridgeite structure

Messaggio da Marco E. Ciriotti » lun 26 feb, 2018 11:51

Prossima pubblicazione.

Referenza:
▪ Grey, I.E., Williams, T., Kampf, A., Cashion, J., Gozukara, Y., MacRae, C., Keck, E. (2018): Non-stoichiometry and local order in minerals with the rockbridgeite structure. European Journal of Mineralogy, 30, (in press).
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

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Marco E. Ciriotti
Messaggi: 24605
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
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Re: Non-stoichiometry and local order in minerals with the rockbridgeite structure

Messaggio da Marco E. Ciriotti » sab 09 giu, 2018 15:15

Referenza:
▪ Grey, I.E., Williams, T., Kampf, A., Cashion, J., Gozukara, Y., MacRae, C., Keck, E. (2018): Non-stoichiometry and local order in minerals with the rockbridgeite structure. European Journal of Mineralogy, 30, (in press).

Abstract:
A non-stoichiometric frondelite from the Hagendorf Süd pegmatite, Bavaria, has been studied using chemical and thermal analyses, electron diffraction (ED), Mössbauer spectroscopy and synchrotron single-crystal structure analysis. The structural formula, with occupancies of the M1, M2 and M3 sites given in sequence, is (Fe3+)(Mn2+0.67Zn0.20Fe2+0.08Fe3+0.70)Σ1.65(Fe3+2.30)(PO4)3(OH)4.9(H2O)0.1. The non-stoichiometric frondelite contains an excess of 0.3 atoms in the M3 site and a deficiency of 0.35 atoms in the M2 site. The ED patterns show rows of reflections that violate the reflection extinctions for Bbmm, and which are due to a local ordering of Fe3+ and vacancies in the M3 sites. Based on the ED results, a model was developed in space group Pnma, in which (100) planes containing corner-shared octahedral dimers of M3 atoms are ordered on a scale of ∼6 nm. The Pnma model was refined successfully against the synchrotron single-crystal data. Non-stoichiometry can be explained within the Pnma local-order model by distortions at the M3 sites in non-stoichiometric regions, where local, barbosalite-like, trimeric chains of face-sharing octahedra are formed.
Marco E. Ciriotti

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