High-Temperature Crystal Chemistry of Meta-Autunite Group Minerals: Metatorbernite, Cu(UO<sub>2</sub>)<sub>2</sub>(PO<sub>4</sub>)<sub>2</sub>(H<sub>2</sub>O)<sub>8</sub> and Metazeunerite, Cu(UO<sub>2</sub>)<sub>2</sub>(AsO<sub>4</sub>)<sub>2</sub>(H<sub>2</sub>O)<sub>8</sub>
Evgeny V. Nazarchuk,
Vladislav V. Gurzhiy,
Yana G. Tagirova,
Dmitri O. Charkin,
Maria G. Krzhizhanovskaya,
Anatoly V. Kasatkin,
Oleg V. Eremin
Affiliations
Evgeny V. Nazarchuk
Department of Crystallography, Saint-Petersburg State University, University Emb. 7/9, St. Petersburg 199034, Russia
Vladislav V. Gurzhiy
Department of Crystallography, Saint-Petersburg State University, University Emb. 7/9, St. Petersburg 199034, Russia
Yana G. Tagirova
Department of Crystallography, Saint-Petersburg State University, University Emb. 7/9, St. Petersburg 199034, Russia
Dmitri O. Charkin
Department of Chemistry, Moscow State University, Vorobievy Gory 1, bd. 3, Moscow 119991, Russia
Maria G. Krzhizhanovskaya
Department of Crystallography, Saint-Petersburg State University, University Emb. 7/9, St. Petersburg 199034, Russia
Anatoly V. Kasatkin
Fersman Mineralogical Museum of the Russian Academy of Sciences, Leninskiy pr. 18, 2, Moscow 119071, Russia
Oleg V. Eremin
Institute of Natural Resources, Ecology and Cryology, Siberian Branch, Russian Academy of Sciences, Nedorezova str. 16a, Chita 672014, Russia
Thermal expansion of metatorbernite, Cu(UO2)2(PO4)2(H2O)8 (1), and metazeunerite, Cu(UO2)2(AsO4)2(H2O)8 (2), has been investigated using single-crystal and powder X-ray diffraction. Both minerals are prone to dehydration, which proceeds already at ambient conditions. According to the single-crystal XRD data, 1 is stable up to 300(50) K, while 2 is stable up to 250(50) K. Powder XRD studies at various temperatures suggest that 1 dehydrates in three stages at ca. 353, 373, and 483 K, while 2 in two stages at ca. 283 and 543 K. Calculation of the main coefficients of thermal expansion reveals strong anisotropy. The expansion is maximal in the direction normal to the autunite-type layers. This correlates with the anisotropy in thermal evolution of Cu–O bond lengths and differences in the thermal behavior of PO4 and AsO4 tetrahedra.
