Crystal structure of uranyl-oxide mineral schoepite

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Marco E. Ciriotti
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Crystal structure of uranyl-oxide mineral schoepite

Messaggio da Marco E. Ciriotti » mar 08 mag, 2018 13:49

Referenza:
▪ Plášil, J. (2018): The crystal structure of uranyl-oxide mineral schoepite, [(UO2)4O(OH)6](H2O)6, revisited. Journal of Geosciences, 63, 65-73.

Abstract:
New single-crystal X-ray diffraction experiments have revealed that the crystal structure of schoepite, one of the more common U-oxide minerals, is centrosymmetric, rather than acentric as reported in the past. Schoepite is orthorhombic, space group Pbca, a = 16.7810(5), b = 14.7044(4), c = 14.2985(5) Å, with V = 3528.22(19) Å3 and Z = 8. Its structure was solved by charge-flipping algorithm and refined to an agreement index (R) of 4.7 % for 4662 unique reflections collected using microfocus X-ray source. Schoepite structure, in line with its previous determination, is based upon U–O–OH sheets of the fourmarierite topology and an interlayer filled only by molecular H2O. The complexity calculations show that the difference in complexity values between schoepite, [(UO2)4O(OH)6](H2O)6, and metaschoepite, [(UO2)4O(OH)6](H2O)5, are much smaller (about 100 bits/cell) then considered previously (about 1000 bits/cell). Such small difference is in line with the easy transformation of schoepite to metaschoepite under ambient conditions and a joint occurrence of both minerals.
Marco E. Ciriotti

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