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High oxide-ion conductivity by the overbonded channel oxygens in Si-deficient La9.565(Si5.8260.174)O26 apatite without interstitial oxygens

Abstract

Apatite-type rare earth silicates are attractive materials with exhaust application such as solid-oxide fuel cells, due to its extremely high oxide-ion conductivity below 600 oC. Interstitial (excess) oxygens have been believed to be responsible for the high conductivity in apatite-type materials. On the contrary, the present study clearly reveals the presence of Si vacancies □ in La-rich La9.565(Si5.8260.174)O26 instead of the interstitial oxygens, by single-crystal neutron and X-ray diffraction analyses, density measurements and ab initio electronic calculations. Higher mobility (lower activation energy) of oxide ions along the c axis is a dominant reason for the high oxide-ion conductivity of La9.565(Si5.8260.174)O26, compared with La9.333Si6O26. The excess La cations yield the overbonded channel oxygens, leading to their highly anisotropic atomic displacements and high oxygen mobility along the c axis. The novel finding of the overbonding effect without interstitial oxygens would open new window in the design of better ion conductors.

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Publication details

The article was accepted on 15 Apr 2018 and first published on 16 Apr 2018


Article type: Paper
DOI: 10.1039/C8TA02237B
Citation: J. Mater. Chem. A, 2018, Accepted Manuscript
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    High oxide-ion conductivity by the overbonded channel oxygens in Si-deficient La9.565(Si5.8260.174)O26 apatite without interstitial oxygens

    K. Fujii, M. Yashima, K. Hibino, M. Shiraiwa, K. Fukuda, S. Nakayama, N. Ishizawa, T. Hanashima and T. Ohhara, J. Mater. Chem. A, 2018, Accepted Manuscript , DOI: 10.1039/C8TA02237B

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