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Issue 23, 2011
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High-resolution 27Al MAS NMR spectroscopic studies of the response of spinel aluminates to mechanical action

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Abstract

The response of the local structure of various types of spinel aluminates, ZnAl2O4 (normal spinel), MgAl2O4 (partly inverse spinel), and Li0.5Al2.5O4 (fully inverse spinel), to mechanical action through high-energy milling is investigated by means of 27Al MAS NMR. Due to the ability of this nuclear spectroscopic technique to probe the local environment of Al nuclei, valuable quantitative insight into the mechanically induced changes in the spinel structure, such as the local cation disorder and the deformation of the polyhedron geometry, is obtained. It is revealed that, independent of the ionic configuration in the initial oxides, the mechanical action tends to randomize cations over the two non-equivalent cation sublattices provided by the spinel structure. The response of the spinels to mechanical treatment is found to be accompanied by the formation of a non-uniform core–shell nanostructure consisting of an ordered crystallite surrounded by a structurally disordered interface/surface shell region. Based on the comparative NMR studies of the non-treated and mechanically treated spinels, an attempt is made to separate the surface effects from the bulk effects in spinel nanoparticles. The non-equilibrium cation distribution and the deformed polyhedra are found to be confined to the near-surface layers of spinel nanoparticles with the thickness extending up to about 0.7 nm. The cation inversion parameter of the mechanically treated spinel is compared with that of the non-treated material at non-ambient conditions.

Graphical abstract: High-resolution 27Al MAS NMR spectroscopic studies of the response of spinel aluminates to mechanical action

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Article information


Submitted
31 Oct 2010
Accepted
20 Dec 2010
First published
24 Jan 2011

J. Mater. Chem., 2011,21, 8332-8337
Article type
Paper

High-resolution 27Al MAS NMR spectroscopic studies of the response of spinel aluminates to mechanical action

V. Šepelák, I. Bergmann, S. Indris, A. Feldhoff, H. Hahn, K. D. Becker, C. P. Grey and P. Heitjans, J. Mater. Chem., 2011, 21, 8332
DOI: 10.1039/C0JM03721D

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