Crystal growth, structure, and superconducting properties of the β -pyrochlore K Os 2 O 6
Crystal growth, structure, and superconducting properties of the β -pyrochlore K Os 2 O 6
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β-烧绿石K Os 2 O 6 的晶体生长、结构和超导性能
DOI：
10.1103/physrevb.73.144506
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发表时间：
2006
影响因子：
3.7
通讯作者：
J. Karpiński
中科院分区：
文献类型：
--
作者：
G. Schuck;S. Kazakov;K. Rogacki;Nikolai Zhigadlo;J. Karpiński
在密封的石英坩埚中生长了KOs_2O_6单晶。详细的单晶X射线衍射研究在室温下显示违反Fd-3 m对称性的布拉格峰。通过比较结构精修，该结构被确定为非中心对称（F-43 m）。与理想的β-烧绿石晶格（Fd-3 m）相比，Os四面体和O八面体网络都表现出呼吸模式般的体积变化，伴随着强烈的各向异性特征的K通道。晶体显示出金属导电性，并在Tc = 9.65 K时急剧转变为超导态。超导性能进行了研究的磁化强度测量温度范围从2至12 K和磁场从0至60 kOe。确定了上临界场Hc ~ 2（T）的温度依赖性，并在T_c附近得到了初始斜率（dHc ~ 2/dT）T_c =-33.3kOe/K。在零温度下的上临界场估计为Hc 2（0）\cong 230 kOe，这是一个接近泡利顺磁极限场Hp（0）\cong 250 kOe的值。计算了KOs 2 O 6的Ginzburg-Landau（GL）相干长度xiGL（0）\约为3.8nm，并得到了Maki参数α\约为\sqrt 2，表明KOs 2 O 6在低温和强磁场下可能表现出反常行为.
Single crystals of KOs2O6 have been grown in a sealed quartz ampoule. Detailed single crystal X-ray diffraction studies at room temperature show Bragg peaks that violate Fd-3m symmetry. With a comparative structure refinement the structure is identified as non-centrosymmetric (F-43m). Compared to the ideal beta-pyrochlore lattice (Fd-3m), both Os tetrahedral and O octahedral network exhibit breathing mode like volume changes accompanied by strong anisotropic character of the K channels. The crystals show metallic conductivity and a sharp transition to the superconducting state at Tc = 9.65 K. Superconducting properties have been investigated by magnetization measurements performed in a temperature range from 2 to 12 K and in magnetic fields from 0 to 60 kOe. The temperature dependence of the upper critical field Hc2(T) has been determined and the initial slope (dHc2/dT)Tc = -33.3 kOe/K has been obtained near Tc. The upper critical field at zero temperature was estimated to be Hc2(0) \cong 230 kOe, which is a value close to the Pauli paramagnetic limiting field Hp(0)\cong 250 kOe. Then, the Ginzburg-Landau (GL) coherence length xi GL(0) \approx 3.8 nm was calculated, and the Maki parameter alpha \approx \sqrt 2 was obtained, suggesting the possibility that KOs2O6 might behave unconventionally at low temperatures and high magnetic fields.