Defect chemistry and oxygen ion migration in the apatite-type materials La9.33Si6O26 and La8Sr2Si6O26

J R Tolchard, M S Islam, P R Slater

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Abstract

Computer modelling techniques have been used to examine the mechanistic features of oxygen ion transport in the La8Sr2Si6O26 and La9.33Si6O26 apatite-oxides at the atomic level. The potential model reproduces the observed complex structures of both phases, which are comprised of [SiO4] tetrahedral units and La/O channels. Defect simulations have examined the lowest energy interstitial and vacancy sites. The results suggest that oxygen ion migration in La8Sr2Si6O26 is via a vacancy mechanism with a direct linear path between O5 sites. Interstitial oxygen migration is predicted for La9.33Si6O26 via a non-linear (sinusoidal-like) pathway through the La3/O5 channel. The simulations demonstrate the importance of local relaxation of [SiO4] tetrahedra to assist in the facile conduction of oxygen interstitial ions. In general, the modelling study confirms that the high ionic conductivity in silicate-based apatites ( with oxygen excess or cation vacancies) is mediated by oxygen interstitial migration.
Original languageEnglish
Pages (from-to)1956-1961
Number of pages6
JournalJournal of Materials Chemistry
Volume13
Issue number8
DOIs
Publication statusPublished - 2003

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