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Could incommensurability in sulfosalts be more common than thought? The case of meneghinite, CuPb 13 Sb 7 S 24
Author(s) -
Bindi Luca,
Petříček Václav,
Biagioni Cristian,
Plášil Jakub,
Moëlo Yves
Publication year - 2017
Publication title -
acta crystallographica section b
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.604
H-Index - 33
ISSN - 2052-5206
DOI - 10.1107/s2052520617002657
Subject(s) - superspace , orthorhombic crystal system , modulation (music) , crystal structure , crystallography , chemistry , displacement (psychology) , group (periodic table) , physics , mathematical physics , psychology , organic chemistry , supersymmetry , acoustics , psychotherapist
The structure of meneghinite (CuPb 13 Sb 7 S 24 ), from the Bottino mine in the Apuan Alps (Italy), has been solved and refined as an incommensurate structure in four‐dimensional superspace. The structure is orthorhombic, superspace group Pnma (0β0)00 s , cell parameters a = 24.0549 (3), b = 4.1291 (6), c = 11.3361 (16) Å, modulation vector q = 0.5433 (4) b* . The structure was refined from 6604 reflections to a final R = 0.0479. The model includes modulation of both atomic positions and displacement parameters, as well as occupational waves. The driving forces stabilizing the modulated structure of meneghinite are linked to the occupation modulation of Cu and some of the Pb atoms. As a consequence of the Cu/[] and Pb/Sb modulations, three‐ to sevenfold coordinations of the M cations (Pb/Sb) occur in different parts of the structure. The almost bimodal distribution of the occupation of Cu/[] and Pb/Sb at M 5 conforms with the coupled substitution Sb 3+ + [] → Pb 2+ + Cu + , thus corroborating the hypothesis deduced previously for the incorporation of copper in the meneghinite structure. The very small departure (∼0.54 versus 0.50) from the commensurate value of the modulation raises the question of whether other sulfosalts considered superstructures have been properly described, and, in this light, if incommensurate modulation in sulfosalts could be much more common than thought.