(Nax□1 - x)5[MnO2]13has been synthesized with x = 0.80 (4), corresponding to Na0.31[MnO2]. This well known material is usually cited as Na0.4[MnO2] and is believed to have a romanèchite-like framework. Here, its true structure is determined, ab initio, by single-crystal electron diffraction tomography (EDT) and refined both by EDT data applying dynamical scattering theory and by the Rietveld method based on synchrotron powder diffraction data (X2= 0.690, Rwp= 0.051, Rp= 0.037, RF2= 0.035). The unit cell is monoclinic C2/m, a = 22.5199 (6), b = 2.83987 (6), c = 14.8815 (4) Å , β = 105.0925 (16)°, V = 918.90 (4) Å3, Z = 2. A hitherto unknown [MnO2] framework is found, which is mainly based on edge- and corner-sharing octahedra and comprises three types of tunnels: per unit cell, two are defined by S-shaped 10-rings, four by eggshaped 8-rings, and two by slightly oval 6-rings of Mn polyhedra. Na occupies all tunnels. The so-determined structure excellently explains previous reports on the electrochemistry of (Na,□)5[MnO2]13. The trivalent Mn3+ions concentrate at two of the seven Mn sites where larger Mn-O distances and Jahn-Teller distortion are observed. One of the Mn3+sites is five-coordinated in a square pyramid which, on oxidation to Mn4+, may easily undergo topotactic transformation to an octahedron suggesting a possible pathway for the transition among different tunnel structures.

Mugnaioli, E., Gemmi, M., Merlini, M., & Gregorkiewitz, M. (2016). (Na,□)5[MnO2]13nanorods: A new tunnel structure for electrode materials determined ab initio and refined through a combination of electron and synchrotron diffraction data. ACTA CRYSTALLOGRAPHICA. SECTION B, STRUCTURAL SCIENCE, CRYSTAL ENGINEERING AND MATERIALS, 72(6), 893-903 [10.1107/S2052520616015651].

(Na,□)5[MnO2]13nanorods: A new tunnel structure for electrode materials determined ab initio and refined through a combination of electron and synchrotron diffraction data

Mugnaioli, Enrico;Gregorkiewitz, Michele
2016

Abstract

(Nax□1 - x)5[MnO2]13has been synthesized with x = 0.80 (4), corresponding to Na0.31[MnO2]. This well known material is usually cited as Na0.4[MnO2] and is believed to have a romanèchite-like framework. Here, its true structure is determined, ab initio, by single-crystal electron diffraction tomography (EDT) and refined both by EDT data applying dynamical scattering theory and by the Rietveld method based on synchrotron powder diffraction data (X2= 0.690, Rwp= 0.051, Rp= 0.037, RF2= 0.035). The unit cell is monoclinic C2/m, a = 22.5199 (6), b = 2.83987 (6), c = 14.8815 (4) Å , β = 105.0925 (16)°, V = 918.90 (4) Å3, Z = 2. A hitherto unknown [MnO2] framework is found, which is mainly based on edge- and corner-sharing octahedra and comprises three types of tunnels: per unit cell, two are defined by S-shaped 10-rings, four by eggshaped 8-rings, and two by slightly oval 6-rings of Mn polyhedra. Na occupies all tunnels. The so-determined structure excellently explains previous reports on the electrochemistry of (Na,□)5[MnO2]13. The trivalent Mn3+ions concentrate at two of the seven Mn sites where larger Mn-O distances and Jahn-Teller distortion are observed. One of the Mn3+sites is five-coordinated in a square pyramid which, on oxidation to Mn4+, may easily undergo topotactic transformation to an octahedron suggesting a possible pathway for the transition among different tunnel structures.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11365/1059946