Formation of apatite oxynitrides by the reaction between apatite-type oxide ion conductors, La{sub 8+x}Sr{sub 2-x}(Si/Ge){sub 6}O{sub 26+x/2}, and ammonia

Journal Article · Tue Dec 15 04:00:00 EST 2009 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2009.09.029· OSTI ID:21372424

Orera, A ^[1]; Headspith, D ^[2]; Apperley, D C ^[3]; Francesconi, M G ^[2]

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1. School of Chemistry, University of Birmingham, Birmingham B15 2TT (United Kingdom)
2. Department of Chemistry, University of Hull, Cottingham Road, Hull (United Kingdom)
3. Department of Chemistry, Durham University, South Road, Durham DH1 3LE (United Kingdom)

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, La{sub 8+x}Sr{sub 2-x}(Si/Ge){sub 6}O{sub 26+x/2,} and NH{sub 3} 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 deg. C, while at higher temperatures (800 deg. C), substantial N incorporation was observed. For the germanate series, partial decomposition was observed after heating in ammonia at 800 deg. C, while at the lower temperature (600 deg. 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 NH{sub 3} at elevated temperatures. - Graphical abstract: In this paper we show that heating the apatite-type electrolytes La{sub 8+x}Sr{sub 2-x}(Si/Ge){sub 6}O{sub 26+x/2} in NH{sub 3} at high temperatures leads to nitridation of the electrolyte, with the level of nitridation increasing with increasing x.

• OSTI ID: 21372424
• Journal Information: Journal of Solid State Chemistry, Journal Name: Journal of Solid State Chemistry Journal Issue: 12 Vol. 182; ISSN 0022-4596; ISSN JSSCBI
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALKALINE EARTH METAL COMPOUNDS
AMMONIA
APATITES
CHEMICAL REACTIONS
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
DIRECT ENERGY CONVERTERS
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
ELECTROCHEMICAL CELLS
FUEL CELLS
GERMANATES
GERMANIUM COMPOUNDS
HEATING
HIGH-TEMPERATURE FUEL CELLS
HYDRIDES
HYDROGEN COMPOUNDS
INTERSTITIALS
IONIC CONDUCTIVITY
LANTHANUM COMPOUNDS
MINERALS
NITRIDATION
NITRIDES
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
OXYGEN COMPOUNDS
PHOSPHATE MINERALS
PHYSICAL PROPERTIES
PNICTIDES
POINT DEFECTS
RARE EARTH COMPOUNDS
SILICATES
SILICON COMPOUNDS
SOLID ELECTROLYTE FUEL CELLS
SOLID OXIDE FUEL CELLS
STRONTIUM COMPOUNDS
TEMPERATURE RANGE
TEMPERATURE RANGE 0400-1000 K
TEMPERATURE RANGE 1000-4000 K
VACANCIES