Browsing by Author "Grey, CP"

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    Controlling the superconductivity of Nb2PdxS5 via reversible Li intercalation
    (American Chemical Society, 2024-01-04) Elgaml, M; Dey, S; Cen, J; Avdeev, M; Scanlon, DO; Grey, CP; Clarke, SJ
    The Nb2PdxS5 (x ≈ 0.74) superconductor with a Tc of 6.5 K is reduced by the intercalation of lithium in ammonia solution or electrochemically to produce an intercalated phase with expanded lattice parameters. The structure expands by 2% in volume and maintains the C2/m symmetry and rigidity due to the PdS4 units linking the layers. Experimental and computational analysis of the chemically synthesized bulk sample shows that Li occupies triangular prismatic sites between the layers with an occupancy of 0.33(4). This level of intercalation suppresses the superconductivity, with the injection of electrons into the metallic system observed to also reduce the Pauli paramagnetism by ∼40% as the bands are filled to a Fermi level with a lower density of states than in the host material. Deintercalation using iodine partially restores the superconductivity, albeit at a lower Tc of ∼5.5 K and with a smaller volume fraction than in fresh Nb2PdxS5. Electrochemical intercalation reproduces the chemical intercalation product at low Li content (<0.4) and also enables greater reduction, but at higher Li contents (≥0.4) accessed by this route, phase separation occurs with the indication that Li occupies another site. © 2024 The Authors. Published by American Chemical Society. This publication is licensed under CC-BY 4.0.
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    Long-range-ordered coexistence of 4-, 5-, and 6-coordinate niobium in the mixed ionic-electronic conductor γ-Ba4Nb2O9
    (American Chemical Society, 2013-07-16) Dunstan, MT; Blanc, F; Avdeev, M; McIntyre, GJ; Grey, CP; Ling, CD
    In a study combining high-resolution single-crystal neutron diffraction and solid-state nuclear magnetic resonance, the mixed ionic-electronic conductor Gamma-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 Gamma-Ba4Nb2O9. © 2013, American Chemical Society.