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Issue 19, 2004
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Doping strategies to optimise the oxide ion conductivity in apatite-type ionic conductors

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Abstract

The apatite-type phases, La9.33+x(Si/Ge)6O26+3x/2, have recently been attracting considerable interest as potential electrolytes for solid oxide fuel cells. In this paper we report results from a range of doping studies in the Si based systems, aimed at determining the key features required for the optimisation of the conductivities. Systems examined have included alkaline earth doping on the rare earth site, and P, B, Ga, V doping on the Si site. By suitable doping strategies, factors such as the level of cation vacancies and oxygen excess have been investigated. The results show that the oxide ion conductivities of these apatite systems are maximised by the incorporation of either oxygen excess or cation vacancies, with the former producing the best oxide ion conductors. In terms of samples containing cation vacancies, conductivities are enhanced by doping lower valent ions, Ga, B, on the Si site. The presence of higher valent ions on these sites, e.g. P, appears to inhibit the incorporation of excess oxygen within the channels, and so limits the maximum conductivity that can be obtained. Overall the results suggest that the tetrahedral sites play a key role in the conduction properties of these materials, supporting recent modelling studies, which have suggested that these tetrahedra aid in the motion of the oxide ions down the conduction channels by co-operative displacements.

Graphical abstract: Doping strategies to optimise the oxide ion conductivity in apatite-type ionic conductors

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Publication details

The article was received on 27 Jan 2004, accepted on 24 Feb 2004 and first published on 03 Aug 2004


Article type: Paper
DOI: 10.1039/B401273A
Dalton Trans., 2004, 3106-3109

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    Doping strategies to optimise the oxide ion conductivity in apatite-type ionic conductors

    A. Najib, J. E. H. Sansom, J. R. Tolchard, P. R. Slater and M. S. Islam, Dalton Trans., 2004, 3106
    DOI: 10.1039/B401273A

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