New hexagonal perovskite with Mn<sup>4+</sup> and Mn<sup>5+</sup> at distinct structural positions
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A new hexagonal perovskite, Ba7Li1.75Mn3.5O15.75, has been synthesised using microwave-assisted solid-state synthesis. Its crystal structure has elements typical for the layered hexagonal perovskites and quasi-one-dimensional oxides, hence representing a new polytype. Structural solution based on simultaneous refinement of X-ray and neutron diffraction data shows that Ba7Li1.75Mn3.5O15.75 crystallizes in a hexagonal unit cell with parameters a = 5.66274(2) Å and c = 16.7467(1) Å (V = 465.063(4) Å3). Columns of face- shared octahedra occupied by Mn4+, Li+ cations and vacancies along the c axis are separated in the ab plane by barium atoms, so that every sixth layer, the coordination of Mn5+ and Li+ changes to tetrahedral. Separation of Mn4+ and Mn5+ cations in two distinct structural positions makes the structure unique. A scanning transmission electron microscopy study revealed the formation of a rhombohedrally centered supercell, which might be attributed to the ordering of manganese and lithium atoms among cationic sites.
AuthorsTarakina, NV; Tyutyunnik, AP; Bazuev, GV; Vasiliev, AD; Berger, IF; Gould, C; Nikolaenko, IV
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