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Issue 23, 2018
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High oxide-ion conductivity in Si-deficient La9.565(Si5.8260.174)O26 apatite without interstitial oxygens due to the overbonded channel oxygens

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Abstract

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

Graphical abstract: High oxide-ion conductivity in Si-deficient La9.565(Si5.826□0.174)O26 apatite without interstitial oxygens due to the overbonded channel oxygens

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Article information


Submitted
09 Mar 2018
Accepted
15 Apr 2018
First published
16 Apr 2018

J. Mater. Chem. A, 2018,6, 10835-10846
Article type
Paper

High oxide-ion conductivity in Si-deficient La9.565(Si5.8260.174)O26 apatite without interstitial oxygens due to the overbonded channel 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, 6, 10835
DOI: 10.1039/C8TA02237B

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