K[(Cu^II,Mn^II,Mn^III)₂(TeO₃)₃·2H₂O,the first zemannite-type structure based on a Jahn-Teller-distorted framework

Autor(en)

Felix Eder, Ronald Miletich, Matthias Weil

Abstrakt

Synthetic single crystals of K[(Cu^II,Mn^II,Mn^III)₂(TeO₃)₃]·2H₂O were obtained from an overconcentrated alkaline aqueous solution in the system K₂O-MnO-CuO-TeO₂ under hydrothermal conditions at T ≤ 220 °C.

Subeuhedral single crystals have been investigated by means of

single-crystal X-ray diffraction. The crystal structure of this new

zemannite-type representative adopts a monoclinic twofold

superstructure. The doubling of the unit-cell volume is accompanied by a

hexagonal-to-monoclinic symmetry reduction, resulting in threefold

twinning with individual crystal domains following the space group

symmetry P2₁. Refinements of site-occupation factors

and the evaluation of bond valences suggest a distribution of di- and

trivalent cations at the octahedrally coordinated M sites with a ratio (Cu^II + Mn^II):Mn^III approximating 1:1. Based on arguments about the cation sizes and the individual bond valence sums, a distribution of Cu^II_1–xMn^III_x and Mn^II_x Mn^III_1–x at each two of the four M sites can be assumed with x between ~ 0.14 and ~ 0.50. The K⁺ cations and H₂O

molecules inside the channels are located off the central channel axis.

In contrast to most other known zemannite-type phases, the

extra-framework atoms show full occupancies and are not disordered. The

distribution of the channel contents supports the anisotropic

deformation of the surrounding framework, which follows the local

symmetry reduction as required for the Jahn-Teller distortion of the

octahedrally coordinated M sites within the framework. The

arrangement of the deformed channels can be understood as the origin of

the existing superstructure.

Organisation(en)

Institut für Mineralogie und Kristallographie

Externe Organisation(en)

Technische Universität Wien

Journal

Mineralogy and Petrology

Band

117

Seiten

133-143

Anzahl der Seiten

11

ISSN

0930-0708

DOI

https://doi.org/10.1007/s00710-022-00808-9

Publikationsdatum

06-2023

Peer-reviewed

Ja

ÖFOS 2012

105116 Mineralogie, 105113 Kristallographie

Schlagwörter

ASJC Scopus Sachgebiete

Geochemistry and Petrology, Geophysics

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/7956cd80-32d7-442b-840d-dc6032d2da2e