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arXiv · 2107.02880

Structural modulation in potassium birnessite single crystals

Liliia D. Kulish·Pavan Nukala·Rick Scholtens·A. G. Mike Uiterwijk·Ruben Hamming-Green·Graeme R. Blake
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Abstract

We report on the growth of single-crystal potassium birnessite (K0.31MnO2*0.41H2O) and present both the average and local structural characterization of this frustrated magnetic system. Single crystals were obtained employing a flux growth method with a KNO3/B2O3 flux at 700 {\deg}C. Single-crystal X-ray diffraction revealed an average orthorhombic symmetry, with space group Cmcm. A combination of high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) with atomic resolution energy dispersive X-ray spectroscopy (EDS) demonstrated the layered structure of potassium birnessite with manganese-containing planes well separated by layers of potassium atoms. MnO6 octahedra and the K/H2O planes were clearly imaged via integrated differential phase contrast (iDPC) STEM. Furthermore, iDPC-STEM also revealed the existence of local domains with alternating contrast of the manganese oxide planes, most likely originating from charge ordering of Mn3+ and Mn4+ along the c-axis. These charge-ordered domains are clearly correlated with a reduction in the c-lattice parameter compared to the rest of the matrix. The insight gained from this work allows for a better understanding of the correlation between structure and magnetic properties.

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Liliia D. Kulish, Pavan Nukala, Rick Scholtens, A. G. Mike Uiterwijk, Ruben Hamming-Green, Graeme R. Blake. 2021-07-06. Structural modulation in potassium birnessite single crystals. https://doi.org/10.1039/d0tc05396a

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