Polytypism in mcalpineite: a study of natural and synthetic Cu3TeO6

Owen P Missen; Stuart J Mills; Stefano Canossa; Joke Hadermann; Gwilherm Nénert; Matthias Weil; Eugen Libowitzky; Robert M Housley; Werner Artner; Anthony R Kampf; Michael S Rumsey; John Spratt; Koichi Momma; Maja A Dunstan

doi:10.1107/S2052520621013032

Polytypism in mcalpineite: a study of natural and synthetic Cu₃TeO₆

Acta Crystallogr B Struct Sci Cryst Eng Mater. 2022 Feb 1;78(Pt 1):20-32. doi: 10.1107/S2052520621013032. Epub 2022 Jan 16.

Authors

Affiliations

¹ School of Earth, Atmosphere and Environment, Monash University, 9 Rainforest Walk, Clayton 3800, Victoria, Australia.
² Geosciences, Museums Victoria, GPO Box 666, Melbourne 3001, Victoria, Australia.
³ EMAT, Department of Physics, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerpen, Belgium.
⁴ Malvern Panalytical B.V., Lelyweg 1, 7602 EA Almelo, The Netherlands.
⁵ Institute for Chemical Technologies and Analytics, Division of Structural Chemistry, TU Wien, Getreidemarkt 9/164-SC, A-1060 Vienna, Austria.
⁶ Institute for Mineralogy and Crystallography, Faculty of Geosciences, Geography and Astronomy, Universität Wien, Althanstr. 14, A-1090 Vienna, Austria.
⁷ Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA.
⁸ X-ray Center, TU Wien, Getreidemarkt 9, A-1060 Vienna, Austria.
⁹ Mineral Sciences Department, Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, CA 90007, USA.
¹⁰ Department of Earth Sciences, Natural History Museum, Cromwell Road, London, SW7 5BD, UK.
¹¹ Core Research Laboratories, Natural History Museum, 21 Cromwell Road, London, UK, SW7 5BD.
¹² National Museum of Nature and Science, 4-1-1 Amakubo, Tsukuba, Ibaraki 305-0005, Japan.
¹³ School of Chemistry, University of Melbourne, Parkville, Victoria, 3010, Australia.

PMID: 35129117
DOI: 10.1107/S2052520621013032

Abstract

Synthetic and naturally occurring forms of tricopper orthotellurate, Cu^II₃Te^VIO₆ (the mineral mcalpineite) have been investigated by 3D electron diffraction (3D ED), X-ray powder diffraction (XRPD), Raman and infrared (IR) spectroscopic measurements. As a result of the diffraction analyses, Cu^II₃Te^VIO₆ is shown to occur in two polytypes. The higher-symmetric Cu^II₃Te^VIO₆-1C polytype is cubic, space group Ia3, with a = 9.537 (1) Å and V = 867.4 (3) Å³ as reported in previous studies. The 1C polytype is a well characterized structure consisting of alternating layers of Cu^IIO₆ octahedra and both Cu^IIO₆ and Te^VIO₆ octahedra in a patchwork arrangement. The structure of the lower-symmetric orthorhombic Cu^II₃Te^VIO₆-2O polytype was determined for the first time in this study by 3D ED and verified by Rietveld refinement. The 2O polytype crystallizes in space group Pcca, with a = 9.745 (3) Å, b = 9.749 (2) Å, c = 9.771 (2) Å and V = 928.3 (4) Å³. High-precision XRPD data were also collected on Cu^II₃Te^VIO₆-2O to verify the lower-symmetric structure by performing a Rietveld refinement. The resultant structure is identical to that determined by 3D ED, with unit-cell parameters a = 9.56157 (19) Å, b = 9.55853 (11) Å, c = 9.62891 (15) Å and V = 880.03 (2) Å³. The lower symmetry of the 2O polytype is a consequence of a different cation ordering arrangement, which involves the movement of every second Cu^IIO₆ and Te^VIO₆ octahedral layer by (1/4, 1/4, 0), leading to an offset of Te^VIO₆ and Cu^IIO₆ octahedra in every second layer giving an ABAB* stacking arrangement. Syntheses of Cu^II₃Te^VIO₆ showed that low-temperature (473 K) hydrothermal conditions generally produce the 2O polytype. XRPD measurements in combination with Raman spectroscopic analysis showed that most natural mcalpineite is the orthorhombic 2O polytype. Both XRPD and Raman spectroscopy measurements may be used to differentiate between the two polytypes of Cu^II₃Te^VIO₆. In Raman spectroscopy, Cu^II₃Te^VIO₆-1C has a single strong band around 730 cm^-1, whereas Cu^II₃Te^VIO₆-2O shows a broad double maximum with bands centred around 692 and 742 cm^-1.

Keywords: 3D ED; copper; crystal structure; mcalpineite; polytypes; tellurate.

MeSH terms

Electrons*
Powder Diffraction
Spectrophotometry, Infrared
Spectrum Analysis, Raman*
X-Ray Diffraction