Oxygen nonstoichiometry and actual Co valence in Na xCoO 2-δ

Maarit Karppinen*, Isao Asako, Teruki Motohashi, Hisao Yamauchi

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

38 Citations (Scopus)

Abstract

The Na xCoO 2-δ system - a host lattice for superb thermoelectrics and parent of the watery CoO 2-layer superconductor - is found to be oxygen nonstoichiometric for x≤0.7, such that with decreasing x, the concentration of oxygen vacancies increases. Accordingly, upon Na deintercalation, the Co valence first increases but does not exceed the value of 3.5. To reveal this, the actual valence of Co was systematically determined by means of wet-chemical redox analysis for a series of Na xCoO 2-δ samples with the Na content x ranging from 0.78 down to 0.12. The low-Na-content samples were obtained from Na-rich ones (0.70≤x≤0.78) through chimie douce extraction of Na utilizing I 2, Br 2, or NO 2BF 4 as an oxidizing agent. For the lowest-Na-content sample of x=0.12, the oxygen nonstoichiometry parameter δ was 0.23. The δ-x relation presently established for a wide x range of Na xCoO 2-δ is indispensable for proper interpretations of physical properties of this system.

Original languageEnglish
Article number092105
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume71
Issue number9
DOIs
Publication statusPublished - 1 Mar 2005
MoE publication typeA1 Journal article-refereed

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