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Synthesis and characterisation of vanadium doped alkaline earth lanthanum germanate oxyapatite electrolyte

Lookup NU author(s): Dr Stevin Pramana

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Abstract

The crystal chemistry and oxygen conductivity of vanadium-doped apatites of nominal composition [La 8AE 2][Ge 6-xV x]O 26+x/2 (AE = Ca, Sr, Ba; 0 ≤ x ≤ 1.5) were studied to establish their potential as intermediate temperature solid oxide fuel cell (SOFC) electrolytes. Single-phase products obtained for x ≤ 0.5 were found, using a combination of powder synchrotron X-ray and neutron diffraction, to be P6 3/m apatites. The ionic conductivities extracted by complex impedance spectroscopy showed that small vanadium amendments enhanced oxygen mobility at intermediate temperatures (500-700 °C) by more than one order of magnitude, as the incorporation of V 5+ through displacement of Ge 4+ is charge balanced with interstitial O 2- that improves ionic conduction. The most promising composition was La 7.88Ca 2Ge 5.35V 0.65O 26.15 that delivered σ = 3.44 × 10 -4 S cm -1 at 500 °C. The superstoichiometric oxygen was delocalised, without fixed X-ray or neutron scattering centres. Crystal chemistry systematics demonstrate that the Ca-apatite was superior because the relatively small framework expanded the tunnel through reduced (La/AE)O 6 metaprism twisting (φ), ensuring the P6 3/m symmetry was adopted, which favours the passage of O 2- with lower activation energy. © 2012 The Royal Society of Chemistry.


Publication metadata

Author(s): Li H, Baikie T, Pramana SS, Shin JF, Slater PR, Brink F, Hester J, Wallwork K, White TJ

Publication type: Article

Publication status: Published

Journal: Journal of Materials Chemistry

Year: 2012

Volume: 22

Issue: 6

Pages: 2658-2669

Print publication date: 14/02/2012

Online publication date: 19/12/2011

ISSN (print): 0959-9428

ISSN (electronic): 1364-5501

Publisher: Royal Society of Chemistry

URL: https://doi.org/10.1039/c1jm13752b

DOI: 10.1039/c1jm13752b


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