New hexagonal perovskite with Mn4+ and Mn5+ at distinct structural positions

Electron Microscopy and Analysis Group Conference 2015

Tarakina, N.V.^1,2 ; Tyutyunnik, A.P.^3 ; Bazuev, G.V.^3 ; Vasiliev, A.D.^4,5 ; Berger, I.F.^3 ; Gould, C.^2 ; Nikolaenko, I.V.^3

NanoVision Centre, School of Engineering and Materials Science, Queen Mary University of London, Mile End, London

E1 4NS, United Kingdom^1

Experimentelle Physik III, Physikalisches Institut and Wilhelm Conrad Rontgen - Research Centre for Complex Material Systems, Universität Wurzburg, Am Hubland, Würzburg

D-97074, Germany^2

Institute of Solid State Chemistry, Ural Branch of the Russian Academy of Sciences, 91 Pervomayskaya, Ekaterinburg

620990, Russia^3

L.V. Kirensky Institute of Physics, Siberian Branch of Russian Academy of Sciences, 50 Akademgorodok, Krasnoyarsk

660036, Russia^4

Siberian Federal University, Svobodny pr. 79, Krasnoyarsk

660041, Russia^5

关键词: Hexagonal perovskite;    Hexagonal unit cells;    Microwave assisted;    Quasi-one dimensional;    Scanning transmission electron microscopy;    Solid-state synthesis;    Structural solutions;    X-Ray and neutron diffraction;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/644/1/012004/pdf
DOI  :  10.1088/1742-6596/644/1/012004

来源: IOP

【 摘 要 】

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 Ba7Li1.75Mn3.5O15.75crystallizes 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.