Oxygen nonstoichiometry and actual Co valence in NaxCoO2-δ -: art. no. 092105

被引：38

作者：

Karppinen, M ^{[1
]}

Asako, I ^{[1
]}

Motohashi, T ^{[1
]}

Yamauchi, H ^{[1
]}

机构：

[1] Tokyo Inst Technol, Mat & Struct Lab, Yokohama, Kanagawa 2268503, Japan

来源：

PHYSICAL REVIEW B | 2005年 / 71卷 / 09期

关键词：

D O I：

10.1103/PhysRevB.71.092105

中图分类号：

T [工业技术];

学科分类号：

08 ;

摘要：

The Na-x,CoO2-delta system-a host lattice for superb thermoelectrics and parent of the watery CoO2-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 NaxCoO2-delta 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 NO2BF4 as an oxidizing agent. For the lowest-Na-content sample of x=0.12, the oxygen nonstoichiometry parameter delta was 0.23. The delta-x relation presently established for a wide x range of NaxCoO2-delta is indispensable for proper interpretations of physical properties of this system.

引用

页数：4

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