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

Citation Shu, G. J. et al. " Oxygen nonstoichiometry and the origin of Na ion ordering in P2-Na_{x}CoO_{2}. " Physical Review B 82.5 (2010): 054106. Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. The impact of oxygen deficiency on physical properties of Na 2/3 CoO 2−␦ has been investigated. From the combined thermogravimetric, magnetic susceptibility, and synchrotron x-ray Laue diffraction studies, it is demonstrated that Na 2/3 CoO 2 shows no superlattice ordering due to Na ions; however Na 2/3 CoO 1.98 , which has the same Co valence as that of Na 0.71 CoO 2 , shows nearly identical magnetic and transport properties and the same simple hexagonal superlattice ordering of ͱ 12a. It is proposed that the Na ion ordering found in Na 2/3 CoO 1.98 is identical to the ideal Na 0.71 CoO 2 of large ͱ 12a ϫ ͱ 12a ϫ 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.