Jump to main content
Jump to site search

Issue 44, 2019
Previous Article Next Article

The layered uranyl silicate mineral uranophane-β: crystal structure, mechanical properties, Raman spectrum and comparison with the α-polymorph

Author affiliations

Abstract

The crystal structure, elastic properties and the Raman spectrum of the layered calcium uranyl silicate pentahydrate mineral uranophane-β, Ca(UO2)2Si2O6(OH)2·5H2O, are studied by means of first-principles solid-state methods and compared with the corresponding information for the α polymorph. The availability of the energy optimized full crystal structure of uranophane-β, including the positions of the hydrogen atoms, made possible the computation of its elastic properties and the Raman spectrum by using the theoretical methodology. An extended set of relevant mechanical data is reported. Uranophane-β is shown to be a weak and ductile mineral and, consequenty, is mechanically very different from the α polymorph which is a hard and brittle material. Uranophane-β exhibits the important negative Poisson's ratio (NPR) and negative linear compressibility (NLC) phenomena. The experimental Raman spectrum of uranophane-β obtained from a natural mineral sample from pegmatite Perus, São Paulo, Brazil, is compared with the spectrum determined theoretically. Since both spectra are in very good agreement, the theoretical methods are employed to assign the Raman spectrum. Three weak bands of the experimental spectrum of this mineral, located at the wavenumbers 2302, 2128 and 2042 cm−1, are identified as combination bands. The Raman spectrum of uranophane-β is also compared with that of the α polymorph. While they are rather similar, a detailed analysis reveals a significant number of differences. Finally, the relative thermodynamic stability of the α and β polymorphs is evaluated. The α polymorph is more stable than the β polymorph at zero pressure and temperature by −12.0 kJ mol−1.

Graphical abstract: The layered uranyl silicate mineral uranophane-β: crystal structure, mechanical properties, Raman spectrum and comparison with the α-polymorph

Back to tab navigation

Supplementary files

Publication details

The article was received on 09 Aug 2019, accepted on 11 Oct 2019 and first published on 14 Oct 2019


Article type: Paper
DOI: 10.1039/C9DT03256H
Dalton Trans., 2019,48, 16722-16736

  •   Request permissions

    The layered uranyl silicate mineral uranophane-β: crystal structure, mechanical properties, Raman spectrum and comparison with the α-polymorph

    F. Colmenero, J. Plášil and J. Sejkora, Dalton Trans., 2019, 48, 16722
    DOI: 10.1039/C9DT03256H

Search articles by author

Spotlight

Advertisements