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Sodium Ion Ordering in NaxCoO2

H. W. Zandbergen·M. L. Foo·Q. Xu·V. Kumar·R. J. Cava
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Abstract

The layered sodium cobalt oxide NaxCoO2 is studied by electron diffraction for a wide range of sodium contents, 0.15<x<0.75. An extensive series of ordered Na ion-Na vacancy superlattices is found beyond the simple hexagonal average structure. The most strongly developed superlattice is found for the composition Na0.5CoO2, which displays Co3+/Co4+ charge ordering at low temperatures. The structural principle for some of the observed ordering schemes, particularly near x=0.5, is, surprisingly, the presence of lines of Na ions and vacancies rather than simply maximized Na-Na separations.

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H. W. Zandbergen, M. L. Foo, Q. Xu, V. Kumar, R. J. Cava. 2004-03-08. Sodium Ion Ordering in NaxCoO2. https://arxiv.org/abs/cond-mat/0403206

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