Evain, M., Petricek, V., Moelo, Y. & Maurel, C. (2006) First (3+2)-dimensional superspace approach to the structure of levyclaudite-(Sb), a member of the cylindrite-type minerals. Acta Crystallogr. Sect. B-Struct. Sci. 62 775–789.
Added by: Florent Boucher (2016-05-12 13:21:36)
|Type de référence: Article
Numéro d'identification (ISBN etc.): 0108-7681
Clé BibTeX: Evain2006a
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Mots-clés: antigorite, chemistry, crystal-structure, electron-microscopy, fepb3sn4sb2s14, franckeite, incommensurate intergrowth compound, Layered compounds, misfit compound, modulated structure
Créateurs: Evain, Maurel, Moelo, Petricek
Collection: Acta Crystallogr. Sect. B-Struct. Sci.
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The structure of synthetic levyclaudite-(Sb), approximately (Pb(1-y)Sb(y)S)(1.357)[Sn(1-x)(Cu(2))(x)S(2)], has been determined by single-crystal X-ray diffraction on the basis of the (3+2)-dimensional superspace approach. This misfit-layer compound, of the cylindrite type, results from the combination of two heavily modulated triclinic Q and H subsystems with a common q wavevector and only one shared reciprocal axis (stacking direction). The Q pseudo-tetragonal layer, similar to(Pb(0.70)Sb(0.30)S), derived from the NaCl archetype, is positively charged; the H pseudo-hexagonal layer, similar to(Sn(0.85)Cu(0.30)S(2)), derived from the CdI(2) archetype, is negatively charged, owing to the replacement of Sn(4+) in an octahedral coordination by Cu(+) pairs in an opposite triangular coordination. The analysis shows a strong transverse displacive modulation of the two layers, referred to as a 'mondulation', correlated to a maximal Sb site occupation factor in the concavity of the Q layer undulation. The wavelength control of the 'mondulation' obeys the vernier principle (14c(Q) congruent to 13c(H)), which would correspond to an energy minimization through a charge transfer density modulation wave, common to all two-dimensional misfit-layer inorganic compounds.
Added by: Florent Boucher