Long-Range-Ordered Coexistence of 4‑, 5‑, and 6‑Coordinate Niobium in the Mixed Ionic-Electronic Conductor γ‑Ba4Nb2O9
datasetposted on 13.08.2013, 00:00 by Matthew T. Dunstan, Frédéric Blanc, Maxim Avdeev, Garry J. McIntyre, Clare P. Grey, Chris D. Ling
In a study combining high-resolution single-crystal neutron diffraction and solid-state nuclear magnetic resonance, the mixed ionic-electronic conductor γ-Ba4Nb2O9 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-Ba4Nb2O9.