Relations structurales entre U3O8 et quelques fluorures mixtes de formules M2M′3F11, MM′2F7 et MM′3F10 |
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Authors: | S Aléonard Y Le Fur JC Champarnaud-Mesjard B Frit MTh Roux |
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Institution: | 1. Laboratoire de Cristallographie, Centre National de la Recherche Scientifique, Laboratoire associé à l''USMG, 166X, 38042 Grenoble Cédex, France |
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Abstract: | U3O8 oxide, as well as M2M′3F11, MM′2F7 and MM′3F10 fluorides, with M = Rb, Tl, Cs, NH4 and M′ = In, Lu, Yb, Tm, is described as the regular repetition according to the … A-A-A … sequence of identical and parallel sheets of edge-and corner-sharing M′F7 or UO7 pentagonal bipyramids and M′F6 octahedra. M′ and U atoms are systematically located at the lattice points of a pseudohexagonal network, but in the fluorides some of these lattice points are vacant, producing hexagonal tunnels in which M atoms are located. It is shown that in the two kinds of compounds the same linear chains and M′3X17 groups of pentagonal bipyramids are present, and that the transformation of the U3O8 structure into the fluorides can be achieved by an ordered substitution of some linear … UOUO … chains by … M-M-M … chains. All these structures can be described with the same structural model based on the chemical twinning principle. |
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