Browsing by Author "Blom, DA"

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    New apatite‐type oxide ion conductor, Bi2La8[(GeO4)6]O3: structure, properties, and direct imaging of low‐level interstitial oxygen atoms using aberration‐corrected scanning transmission electron microscopy
    (Wiley, 2017-02-23) Tate, ML; Blom, DA; Avdeev, M; Brand, HEA; McIntyre, GJ; Vogt, T; Evans, IR
    The new solid electrolyte Bi2La8[(GeO4)6]O3 is prepared and characterized by variable‐temperature synchrotron X‐ray and neutron diffraction, aberration‐corrected scanning transmission electron microscopy, and physical property measurements (impedance spectroscopy and second harmonic generation). The material is a triclinic variant of the apatite structure type and owes its ionic conductivity to the presence of oxide ion interstitials. A combination of annular bright‐field scanning transmission electron microscopy experiments and frozen‐phonon multislice simulations enables direct imaging of the crucial interstitial oxygen atoms present at a level of 8 out of 1030 electrons per formula unit of the material, and crystallographically disordered, in the unit cell. Scanning transmission electron microscopy also leads to a direct observation of the local departures from the centrosymmetric average structure determined by diffraction. As no second harmonic generation signal is observed, these displacements are non‐cooperative on the longer length scales probed by optical methods. © 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim
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    Structure, stability, and photoluminescence in the anti-perovskites Na3W1−xMoxO4F (0≤x≤1)
    (Elsevier, 2015-10-01) Sullivan, E; Avdeev, M; Blom, DA; Gahrs, CJ; Green, RL; Hamaker, CG; Vogt, T
    Single-phase ordered oxyfluorides Na3WO4F, Na3MoO4F and their mixed members Na3W1−xMoxO4F can be prepared via facile solid state reaction of Na2MO4·2H2O (M=W, Mo) and NaF. Phases produced from incongruent melts are metastable, but lower temperatures allow for a facile one-step synthesis. In polycrystalline samples of Na3W1−xMoxO4F, the presence of Mo stabilizes the structure against decomposition to spinel phases. Photoluminescence studies show that upon excitation with λ=254 nm and λ=365 nm, Na3WO4F and Na3MoO4F exhibit broad emission maxima centered around 485 nm. These materials constitute new members of the family of self-activating ordered oxyfluoride phosphors with anti-perovskite structures which are amenable to doping with emitters such as Eu3+. © 2015 Elsevier Inc.