Na order and Co charge disproportionation in Na sub(x)CoO sub(2)

We have synthesized and characterized different stable phases of sodium cobaltates Na sub(x)CoO sub(2) with sodium content 0.65 < x < 0.80. We demonstrate that super(23)Na NMR allows us to determine the difference in the susceptibility of the phases and reveals the presence of Na order in each...

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Bibliographic Details
Published in:Physica. B, Condensed matter Condensed matter, 2015-03, Vol.460, p.58-63
Main Authors: Mukhamedshin, I R, Alloul, H
Format: Article
Language:English
Subjects:
Charge
Cobalt
Condensed matter
Disproportionation
Magnetic properties
Nuclear magnetic resonance
Phases
Sodium
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Summary:We have synthesized and characterized different stable phases of sodium cobaltates Na sub(x)CoO sub(2) with sodium content 0.65 < x < 0.80. We demonstrate that super(23)Na NMR allows us to determine the difference in the susceptibility of the phases and reveals the presence of Na order in each phase. super(59)Co NMR experiments give clear evidence that Co charge disproportionation is a dominant feature of Na cobaltates. Only a small fraction ([approximate] 25%) of cobalt are in a non-magnetic Co super(3+) charge state whereas electrons delocalize on the other cobalt. The magnetic and charge properties of the different Co sites are highly correlated with each other as their magnetic shift K sub(ZZ) scales linearly with their quadrupolar frequency [nu] sub(Q). This reflects the fact that the hole content on the Co orbitals varies from site to site. The unusual charge differentiation found in this system calls for better theoretical understanding of the incidence of the Na atomic order on the electronic structures of these compounds.
ISSN:0921-4526
DOI:10.1016/j.physb.2014.11.040