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Polytypism in mcalpineite: a study of natural and synthetic Cu3TeO6

Citation

Missen, OP and Mills, SJ and Canossa, S and Hadermann, J and Nenert, G and Weil, M and Libowitzky, E and Housley, RM and Artner, W and Kampf, AR and Rumsey, MS and Spratt, J and Momma, K and Dunstan, MA, Polytypism in mcalpineite: a study of natural and synthetic Cu3TeO6, Acta Crystallographica, 78, (1) pp. 20-32. ISSN 2052-5206 (2021) [Refereed Article]


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PDF (Characterisation of two forms of copper tellurate, previously thought to be just one polytype. Cu3TeO6 is an important antiferromagnet.)
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DOI: doi:10.1107/S2052520621013032

Abstract

Synthetic and naturally occurring forms of tricopper orthotellurate, CuII3TeVIO6 (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, CuII3TeVIO6 is shown to occur in two polytypes. The higher-symmetric CuII3TeVIO6-1C polytype is cubic, space group Ia3, with a = 9.537 (1)  and V = 867.4 (3) 3 as reported in previous studies. The 1C polytype is a well characterized structure consisting of alternating layers of CuIIO6 octahedra and both CuIIO6 and TeVIO6 octahedra in a patchwork arrangement. The structure of the lower-symmetric orthorhombic CuII3TeVIO6-2O 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) , b = 9.749 (2) , c = 9.771 (2)  and V = 928.3 (4) 3. High-precision XRPD data were also collected on CuII3TeVIO6-2O 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) , b = 9.55853 (11) , c = 9.62891 (15)  and V = 880.03 (2) 3. The lower symmetry of the 2O polytype is a consequence of a different cation ordering arrangement, which involves the movement of every second CuIIO6 and TeVIO6 octahedral layer by (1/4, 1/4, 0), leading to an offset of TeVIO6 and CuIIO6 octahedra in every second layer giving an ABAB* stacking arrangement. Syntheses of CuII3TeVIO6 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 CuII3TeVIO6. In Raman spectroscopy, CuII3TeVIO6-1C has a single strong band around 730 cm−1, whereas CuII3TeVIO6-2O shows a broad double maximum with bands centred around 692 and 742 cm−1.

Item Details

Item Type:Refereed Article
Keywords:mcalpineite; copper; tellurate; polytypes; crystal structure; 3D ED
Research Division:Earth Sciences
Research Group:Geology
Research Field:Mineralogy and crystallography
Objective Division:Mineral Resources (Excl. Energy Resources)
Objective Group:Other mineral resources (excl. energy resources)
Objective Field:Other mineral resources (excl. energy resources) not elsewhere classified
UTAS Author:Missen, OP (Dr Owen Missen)
ID Code:154972
Year Published:2021
Web of Science® Times Cited:1
Deposited By:CODES ARC
Deposited On:2023-01-20
Last Modified:2023-01-25
Downloads:0

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