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Search for new materials and properties in the pyrochlore oxides

寻找烧绿石氧化物的新材料和新性能

基本信息

批准号：
16340101
负责人：
HIROI Zenji
金额：
$ 9.92万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2004
资助国家：
日本
起止时间：
2004 至 2006
项目状态：
已结题

项目摘要

The study of non-Cu-based oxide superconductors has been extended during the last decade, aiming at understanding the role of electron correlations in the mechanism of superconductivity or searching for a novel pairing mechanism, hopefully to reach a higher Tc. An interesting example recently found is a family of pyrochlore oxide superconductors. The first discovered is a-pyrochlore rhenate Cd_2Re_2O_7 with T_c = 1.0 K and the second β-pyrochlore osmate AOs_2O_6 with T_c = 3.3, 6.3, and 9.6 K for A = Cs, Rb, and K, respectively. They crystallize in the cubic pyrochlore structure of space group Fd-3m and commonly possess a 3D skeleton made of ReO_6 or OsO_6 octahedra. The "pyrochlore" sublattice occupied by the transition metal ions is comprised of corner-sharing tetrahedra that are known to be highly frustrating for a localized spin system with antiferromagnetic nearest-neighbor interactions.Chemical trends of fundamental superconducting parameters and normal-state properties are studied for a family of pyrochlore oxide superconductors. Particularly, the change of T_c from 1.0 K for α-pyrochlore Cd_2Re_2O_7 to 3.3 K (A = Cs), 6.3 K (Rb), and 9.6 K (K) for β-pyrochlore AOs_2O_6 is discussed on the basis of the conventional BCS scheme. Enhanced T_c and anomalous features observed for KOs_2O_6 are ascribed to low-energy phonons probably coming from the rattling of the K cations.

近十年来，非铜基氧化物超导体的研究得到了扩展，旨在了解电子相关性在超导机制中的作用或寻找新的配对机制，以期达到更高的Tc。最近发现的一个有趣的例子是烧绿石氧化物超导体家族。第一个发现是α-烧绿石铼酸Cd_2Re_2O_7，T_c = 1.0 K；第二个是β-烧绿石锇酸AOs_2O_6，T_c = 3.3、6.3和9.6 K，A = Cs、Rb和K。它们以空间群Fd-3m的立方烧绿石结构结晶，通常具有由ReO_6或OsO_6八面体组成的3D骨架。过渡金属离子占据的“烧绿石”亚晶格由共享角的四面体组成，已知这种四面体对于具有反铁磁最近邻相互作用的局域自旋系统来说是非常令人沮丧的。研究了一系列烧绿石氧化物超导体的基本超导参数和正常状态特性的化学趋势。特别是在传统BCS方案的基础上，讨论了T_c从α-烧绿石Cd_2Re_2O_7的1.0 K到β-烧绿石AOs_2O_6的3.3 K（A = Cs）、6.3 K（Rb）和9.6 K（K）的变化。 KOs_2O_6 观察到的 T_c 增强和异常特征归因于可能来自 K 阳离子振动的低能声子。