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Next‐near‐neighbour interactions with Al in Li + ‐ and Rb + ‐exchanged Na + β‐aluminas, detected by synchrotron X‐ray absorption spectroscopy
Author(s) -
Marcelli Augusto,
Mottana Annibale,
Cibin Giannantonio
Publication year - 2000
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s0021889899015654
Subject(s) - xanes , crystallography , alkali metal , atom (system on chip) , chemistry , absorption spectroscopy , corundum , octahedron , absorption (acoustics) , spectral line , crystal structure , materials science , mineralogy , physics , optics , computer science , composite material , embedded system , astronomy , organic chemistry
Synchrotron X‐ray absorption near‐edge structure (XANES) spectroscopy studies have been carried out on the electronic and crystal structure environments around the Al atom in Na + β‐alumina and in two β‐aluminas with Na + exchanged by Li + and Rb + . The aim is to define the type of interaction, if any, existing between the Al located in the `spinel block' and the fast‐conducting cations in the `conduction plane'. Na + β′′‐alumina has also been studied for comparison. All β‐alumina spectra differ from that of α‐alumina (corundum) by showing additional features due to the presence of tetrahedral Al. Moreover, they all show a much greater degree of local disorder. There are definite, but small, interactions between tetrahedral Al (and, possibly, also octahedral Al) in the `spinel block' and the Na + and Rb + cations in the `conduction plane'; Na + and Rb + β‐aluminas have similar Al K ‐edge XANES features, but with intensities that change in relation to the weight of the `conduction plane' atom. Despite differences in composition and structure, Na + β′′‐alumina shows the same behaviour, thus confirming the substantial similarity of the Al local environments. Li + ‐exchanged β‐alumina has an Al K ‐edge XANES spectrum that apparently differs from all others, but actually conveys the same basic information. Indeed, interaction between Al and Li is much greater than in any other β‐alumina because Li + moves laterally off the `conduction plane' to become close to a facing tetrahedral Al, and strongly interacts with it. Thus, this study also draws attention to the fact that β‐aluminas react differently to alkali exchange.