Dunstan, Matthew T. Blanc, Frédéric Avdeev, Maxim McIntyre, Garry J. Grey, Clare P. Ling, Chris D. Long-Range-Ordered Coexistence of 4‑, 5‑, and 6‑Coordinate Niobium in the Mixed Ionic-Electronic Conductor γ‑Ba<sub>4</sub>Nb<sub>2</sub>O<sub>9</sub> In a study combining high-resolution single-crystal neutron diffraction and solid-state nuclear magnetic resonance, the mixed ionic-electronic conductor γ-Ba<sub>4</sub>Nb<sub>2</sub>O<sub>9</sub> is shown to have a unique structure type, incorporating niobium in 4-, 5-, and 6-coordinate environments. The 4- and 5-coordinate niobium tetrahedra and trigonal bipyrimids exist in discrete layers, within and among which their orientations vary systematically to form a complex superstructure. Through analysis and comparison of data obtained from hydrated versus dehydrated samples, a mechanism is proposed for the ready hydration of the material by atmospheric water. This mechanism, and the resulting hydrated structure, help explain the high protonic and oxide ionic conductivity of γ-Ba<sub>4</sub>Nb<sub>2</sub>O<sub>9</sub>. 4Nb;Ba;mechanism;structure type;niobium tetrahedra 2013-08-13
    https://acs.figshare.com/articles/dataset/Long_Range_Ordered_Coexistence_of_4_5_and_6_Coordinate_Niobium_in_the_Mixed_Ionic_Electronic_Conductor_Ba_sub_4_sub_Nb_sub_2_sub_O_sub_9_sub_/2387818
10.1021/cm4014656.s002