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Formation of apatite oxynitrides by the reaction between apatite-type oxide ion conductors, La8+xSr2-x(Si/Ge)6O26+x/2, and ammonia

Francesconi, G; Orera, A.; Headspith, D.; Francesconi, M. G.; Apperley, D. C.; Francesconi, M. Grazia; Slater, P. R.

Authors

G Francesconi

A. Orera

D. Headspith

M. G. Francesconi

D. C. Apperley

P. R. Slater



Abstract

Following growing interest in the use of ammonia as a fuel in solid oxide fuel cells (SOFCs), we have investigated the possible reaction between the apatite silicate/germanate electrolytes, La8+xSr2−x(Si/Ge)6O26+x/2, and NH3 gas. We examine how the composition of the apatite phase affects the reaction with ammonia. For the silicate series, the results showed a small degree of N incorporation at 600°C, while at higher temperatures (800°C), substantial N incorporation was observed. For the germanate series, partial decomposition was observed after heating in ammonia at 800°C, while at the lower temperature (600°C), significant N incorporation was observed. For both series, the N content in the resulting apatite oxynitride was shown to increase with increasing interstitial oxide ion content (x/2) in the starting oxide. The results suggest that the driving force for the nitridation process is to remove the interstitial anion content, such that for the silicates the total anion (O+N) content in the oxynitrides approximates to 26.0, the value for an anion stoichiometric apatite. For the germanates, lower total anion contents are observed in some cases, consistent with the ability of the germanates to accommodate anion vacancies. The removal of the mobile interstitial oxide ions on nitridation suggests problems with the use of apatite-type electrolytes in SOFCs utilising NH3 at elevated temperatures.

Journal Article Type Article
Publication Date 2009-12
Journal Journal of Solid State Chemistry
Print ISSN 0022-4596
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 182
Issue 12
Pages 3294-3298
APA6 Citation Orera, A., Headspith, D., Apperley, D. C., Francesconi, M. G., & Slater, P. R. (2009). Formation of apatite oxynitrides by the reaction between apatite-type oxide ion conductors, La8+xSr2-x(Si/Ge)6O26+x/2, and ammonia. Journal of Solid State Chemistry, 182(12), 3294-3298. doi:10.1016/j.jssc.2009.09.029
DOI https://doi.org/10.1016/j.jssc.2009.09.029
Keywords Physical and Theoretical Chemistry; Inorganic Chemistry; Materials Chemistry; Electronic, Optical and Magnetic Materials; Condensed Matter Physics; Ceramics and Composites
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