Oxygen nonstoichiometry and actual Co valence inNaxCoO2−δ
Oxygen nonstoichiometry and actual Co valence inNaxCoO2−δ
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DOI：
10.1103/physrevb.71.092105
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发表时间：
2005-03
影响因子：
3.7
通讯作者：
M. Karppinen;Isao Asako;T. Motohashi;H. Yamauchi
中科院分区：
文献类型：
--
作者：
M. Karppinen;Isao Asako;T. Motohashi;H. Yamauchi
该系统——超级热电材料的主晶格和水层超导体的母体——被发现是氧非化学计量的，因此随着氧空位浓度的降低，氧空位的浓度会增加。因此，当Na脱嵌时，Co价首先增加，但不超过3.5的值。为了揭示这一点，通过湿化学氧化还原分析对 Na 含量从 0.78 到 0.12 的一系列样品系统地确定了 Co 的实际价态。低Na含量样品是通过利用化学法提取Na或作为氧化剂从富Na样品中获得的。对于钠含量最低的样品，氧非化学计量参数为0.23。目前为广泛建立的关系对于正确解释该系统的物理性质是必不可少的。
Thesystem—a host lattice for superb thermoelectrics and parent of the watery-layer superconductor—is found to be oxygen nonstoichiometric for, such that with decreasing, 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 ofsamples with the Na contentranging from 0.78 down to 0.12. The low-Na-content samples were obtained from Na-rich onesthroughchimie douceextraction of Na utilizing,, oras an oxidizing agent. For the lowest-Na-content sample of, the oxygen nonstoichiometry parameterwas 0.23. Therelation presently established for a widerange ofis indispensable for proper interpretations of physical properties of this system.