Effects of A- and B-site (co-)acceptor doping on the structure and proton conductivity of LaNbO4

M. Ivanova, Sandrine Ricote, W.A. Meulenberg, R. Haugsrud, M. Ziegner

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    Abstract

    B-site and A- and B-site co-doped lanthanum niobates, La(1-x)DA(x)Nb(1-y)DB(y)O(4-δ), where DA stands for Ca or Ba and DB for Ga, Ge or In (x = 0 or 0.01; y = 0.01), have been synthesized via the solid-state route. Essentially single-phase materials were obtained after 10 h at 1500 °C with monoclinic Fergusonite structure at room temperature. The unit cell volume increases slightly with the presence of the acceptor. The electrical conductivity of the materials, characterized as a function of the temperature from 300 °C to 900 °C under wet reducing conditions with AC impedance spectroscopy, was dominated by protons. The maximum conductivity of 4.1 · 10−4 S · cm−1 at 900 °C was obtained for La0.99Ca0.01Nb0.99Ga0.01O4-δ, which is a factor of ~ 2.5 lower than the highest conductivity reported for the A-site Ca-doped LaNbO4. Based on a semi-quantitative evaluation it was shown that the hydration of the B-site and A- and B-site co-doped LaNbO4 is slightly more exothermic and that the proton mobility has higher activation enthalpies than Ca-doped LaNbO4. This is accounted for by a stronger association between the acceptor and the proton for B-site than for A-site doping.
    Original languageEnglish
    JournalSolid State Ionics
    Volume213
    Pages (from-to)45-52
    ISSN0167-2738
    DOIs
    Publication statusPublished - 2012
    Event15th International Conference on Solid State Protonic Conductors - Santa Barbara, CA, United States
    Duration: 15 Aug 201019 Aug 2010

    Conference

    Conference15th International Conference on Solid State Protonic Conductors
    CountryUnited States
    CitySanta Barbara, CA
    Period15/08/201019/08/2010

    Keywords

    • Proton-conducting ceramic materials
    • Rare earth ortho-niobates
    • Acceptor-doped lanthanum niobate

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