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2010 | 117 | 1 | 38-41
Article title

Disorder and Diffusion in Mayenite

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EN
Abstracts
EN
Mayenite, Ca_{12}Al_{14}O_{33}, has attracted enormous attention for novel technological applications after the discovery of its high oxygen ionic conductivity. The crystal structure consists of a calcium-aluminate framework, comprising 32 of the 33 oxygen anions. The remaining oxygen is distributed over 1/6 of large cages within the framework. The true structure is heavily disordered and usually non-stoichiometric due to the presence of extra anions and is presented for four samples: pure oxygen mayenite (O-mayenite), partly (O/N-mayenite) and fully (N-mayenite) exchanged by nitrogen and doped with iron (Fe-mayenite). All samples were investigated by neutron powder diffraction up to 1050°C. Data were analysed by the Rietveld method and by difference Fourier methods. As prepared O-mayenite contains O_{2}^{-} and OH^{-}, N- and O/N-mayenite also NH_{2}^{-}, NH^{2-} and N^{3-}, while Fe-mayenite was free of extra radicals. In O- and N-mayenite the extra species are lost under vacuum conditions above ca. 700°C, whereas O/N-mayenite retained NH_{2}^{-} up to high temperatures. Diffusion of oxygen proceeds via a jump-like interstitialcy process involving exchange of the "free" oxygen with framework oxygen, coupled to relaxations of Ca ions. In O/N-mayenite NH_{2}^{-} diffuses via interstitial process. In Fe-mayenite encaged oxygen is "invisible" due to extreme delocalisation or loss.
Keywords
EN
Contributors
author
  • Department für Geo- und Umweltwissenschaften, Sektion Kristallographie, LMU München, Am Coulombwall 1, 85748 Garching, Germany
  • Department für Geo- und Umweltwissenschaften, Sektion Kristallographie, LMU München, Am Coulombwall 1, 85748 Garching, Germany
author
  • Institut für Chemie, TU Berlin, Str. des 17. Juni 135, 10623 Berlin, Germany
author
  • Institut für Chemie, TU Berlin, Str. des 17. Juni 135, 10623 Berlin, Germany
author
  • TU Darmstadt, Institute of Materials Science, Petersenstr. 23, 64287 Darmstadt, Germany
author
  • TU Darmstadt, Institute of Materials Science, Petersenstr. 23, 64287 Darmstadt, Germany
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Document Type
Publication order reference
Identifiers
YADDA identifier
bwmeta1.element.bwnjournal-article-appv117z108kz
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