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Issue 14, 2010
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Protonic defects and water incorporation in Si and Ge-based apatite ionic conductors

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Abstract

Apatite-type oxide-ion conductors have attracted considerable interest as potential fuel cell electrolytes. Atomistic modelling techniques have been used to investigate oxygen interstitial sites, protonic defects and water incorporation in three silicate and three germanate-based apatite-systems, namely La8Ba2(SiO4)6O2, La9.33(SiO4)6O2, La9.67(SiO4)6O2.5, La8Ba2(GeO4)6O2, La9.33(GeO4)6O2, and La9.67(GeO4)6O2.5. The simulation models reproduce the complex experimental structures for all of these systems. The interstitial defect simulations have examined the lowest energy configuration and confirm this site to be near the Si/GeO4 tetrahedra. The water incorporation calculations identify the O–H protonic site to be along the O4 oxygen channel as seen in naturally occurring hydroxy-apatites. The results also show more favourable and exothermic water incorporation energies for the germanate-based apatites. This is consistent with recent experimental work, which shows that Ge-apatites take up water more readily than the silicate analogues.

Graphical abstract: Protonic defects and water incorporation in Si and Ge-based apatite ionic conductors

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Article information


Submitted
18 Nov 2009
Accepted
12 Jan 2010
First published
18 Feb 2010

J. Mater. Chem., 2010,20, 2766-2772
Article type
Paper

Protonic defects and water incorporation in Si and Ge-based apatite ionic conductors

P. M. Panchmatia, A. Orera, E. Kendrick, J. V. Hanna, M. E. Smith, P. R. Slater and M. S. Islam, J. Mater. Chem., 2010, 20, 2766
DOI: 10.1039/B924220A

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