title: Sodium manganese fluorosulfate with a triplite structure.
abstract: The crystal structure of the NaMnSO4F fluorosulfate phase prepared by low-temperature solid-state synthesis has been solved and refined by the Rietveld analysis of synchrotron X-ray powder diffraction data. Isostructural to the naturally occurring triplite family of minerals, this compound crystallizes in monoclinic C2/c symmetry (No. 15) with unit-cell parameters of a = 13.77027 (17), b = 6.63687 (8), c = 10.35113 (14) Å, β = 121.4795 (3)° and V = 806.78 (2) Å(3). Its structure is built of edge-sharing chains of distorted MO4F2 octahedra, which are interconnected by constituent SO4 tetrahedra to form a robust three-dimensional polyanionic framework. MO4F2 octahedra are randomly occupied by Na and Mn with close to 1:1 occupancy. This random mixing of cations among polyhedral building blocks means that there are no channels for Na-ion conduction, rendering it electrochemically inactive. The structure is discussed and compared with other known alkali metal fluorosulfates as well as to naturally occurring triplite-type minerals.
authors.affiliation: Department of Chemical System Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
authors.forename: Prabeer
authors.initials: P
authors.lastname: Barpanda
authors.forename: Chris D
authors.initials: CD
authors.lastname: Ling
authors.forename: Gosuke
authors.initials: G
authors.lastname: Oyama
authors.forename: Atsuo
authors.initials: A
authors.lastname: Yamada
keywords: disorder; fluorosulfates; sodium-ion battery cathodes; triplite