Cation ordering, valence states and symmetry breaking in the crystal-chemically complex mineral chevkinite-(Ce)

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Marco E. Ciriotti
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Iscritto il: ven 25 giu, 2004 11:31
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Cation ordering, valence states and symmetry breaking in the crystal-chemically complex mineral chevkinite-(Ce)

Messaggio da Marco E. Ciriotti » ven 12 lug, 2019 11:21

Prossima pubblicazione.

Referenza:
▪ Stachowicz, M., Welch, M.D., Bagiński, B., Kartashov, P.M., Macdonald, R., Woźniak, K. (2019): Cation ordering, valence states and symmetry breaking in the crystal-chemically complex mineral chevkinite-(Ce). Recrystallization, transformation and metamict states in chevkinite. American Mineralogist, 104, (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: 26121
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
Contatta:

Re: Cation ordering, valence states and symmetry breaking in the crystal-chemically complex mineral chevkinite-(Ce)

Messaggio da Marco E. Ciriotti » lun 14 ott, 2019 19:55

Referenza:
▪ Stachowicz, M., Welch, M.D., Bagiński, B., Kartashov, P.M., Macdonald, R., Woźniak, K. (2019): Cation ordering, valence states and symmetry breaking in the crystal-chemically complex mineral chevkinite-(Ce). Recrystallization, transformation and metamict states in chevkinite. American Mineralogist, 104, 1481–1486.

Abstract:
Annealing is commonly used in the recrystallization of metamict minerals in an attempt to reconstruct the original structure. Annealing at 750 °C of Nb-rich chevkinite-(Ce) from the Biraya rare-metal deposit, Russia, resulted in the structural transformation C2/m → P21/a, which defines chevkinite stability in different environments. This transformation seems to be a rapid version of a naturally occurring process that possibly involves twinning of the crystals. Nb-rich chevkinite-(Ce) occurs naturally as two polymorphs, one with the C2/m space group and the other with P21/a. The latter is the stable form under ambient conditions. There are some distinct differences in the values of the structural parameters, such as the average M-O distances or site scattering values of particular sites for both space groups, which can be associated with the redistribution of some lighter cations, mainly Mg2+, within the crystal lattice. The use of complementary experimental techniques (electron probe microanalysis, X‑ray diffraction, and photoelectron spectroscopy) has delivered information on the structure and transformation of a very complex, highly zoned and partially metamict solid solution. It should be useful in determining the structure of any mineral where cation disorder is present.
Marco E. Ciriotti

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