Oxygen non-stoichiometry and the origin of Na ion ordering in P2-NaxCoO2

Abstract

The impact of oxygen deficiency on physical properties of Na2/3CoO2-x has been investigated. From the combined thermogravimetric, magnetic susceptibility and synchrotron X-ray Laue diffraction studies, it is demonstrated that Na2/3CoO2 shows no superlattice ordering due to Na ions; however Na2/3CoO1.98, which has the same Co valence as that of Na0.71CoO2, shows nearly identical magnetic and transport properties and the same simple hexagonal superlattice ordering of sqrt(12)a. It is proposed that the Na ion ordering found in Na2/3CoO1.98 is identical to the ideal Na0.71CoO2 of large sqrt(12)a x sqrt(12)a x 3c superlattice but with additional Na vacancies which are bound to the oxygen defects at room temperature. We conclude that oxygen vacancies play a key role in stabilizing the superlattice structure and must be accounted for in its modeling.

arXiv comment5 pages, 4 figures

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Cited by in corpus (5)

• 59Co NMR evidence for charge and orbital order in the kagome like structure of Na2/3CoO2
• Electronic phase diagram of LixCoO2 revisited with potentiostatically de-intercalated single crystals
• Theoretical analysis of oxygen vacancies in layered sodium cobaltate Na_xCoO_{2-δ}
• Theory of carrier concentration-dependent electronic behavior in layered cobaltates
• Enhanced low energy fluctuations and increasing out-of-plane coherence in vacancy ordered NaxCoO2