Thermal behavior of uranyl selenite minerals derriksite and demesmaekerite

[摘要] Crystal structures of two uranyl selenite minerals derriksite, Cu4[(UO2)(SeO3)2](OH)6, and demesmaekerite,Pb2Cu5[(UO2)2(SeO3)6(OH)6](H2O)2, which structures are based on uranyl selenite 1D structural units, were studiedemploying single-crystal X-ray diffraction analysis at various temperatures. The refinement of their crystal structuresreveals the detailed dynamics of the interatomic interactions during the heating process, which allows describing thethermal behavior. Uranyl selenite chains and their mutual arrangement mainly provide the rigidity of the crystal structure.Thus the lowest expansion in the structure of derriksite is observed along the direction of uranyl selenite chains, whilethe largest expansion occurs in the direction normal to chains, with the space occupied by lone electron pairs of Se4+atoms and low covalent bond distribution density. The maximal expansion in the crystal structure of demesmaekerite ismanifested approximately along the [100], which matches the direction of chains of less strongly bonded Cu-centeredoctahedra, and gaps between Cu chains occupied by the Pb cations. The crystal structure of demesmaekerite undergoescontraction in the direction of the space between the U-bearing chains with the deficiency of strong covalent bonds.Contraction of the structure can also be attributed to the orthogonalization of the oblique triclinic angles of the unitcell. It is demonstrated that the assignment of U-bearing units during structure description is reasonably justified since,regardless of their dimensionality, these substructural units are one of the most stable and rigid blocks in the structuralarchitecture, and they govern the thermal behavior of the entire structure.

[学科分类] 自动化工程

[关键词] derriksite;demesmaekerite;uranyl;selenite;crystal structure;thermal expansion