Out-of-plane effect on the superconductivity of Sr2-xBaxCuO3+δ with Tc up to 98 K
Out-of-plane effect on the superconductivity of Sr2-xBaxCuO3+δ with Tc up to 98 K
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DOI：
10.1103/physrevb.80.094523
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发表时间：
2009-09-01
影响因子：
3.7
通讯作者：
Uchida, S.
中科院分区：
文献类型：
--
作者：
Gao, W. B.;Liu, Q. Q.;Uchida, S.
采用高压高温合成法制备了一系列新的Sr_（2-x）CuO_（3+）δ（0 < x < 0.6）超导体。的Rietveld细化的基础上，粉末X射线衍射证实，超导体结晶在K2 NiF 4型结构的空间群I4/mmm类似的La 2CuO 4，但部分占据顶端的氧网站。结果表明，Ba取代的Sr_2CuO_3 ~+ δ超导体的超导转变温度T-c随载流子掺杂量的增加而增大，常数δ不仅受顶部O原子的有序/无序控制，而且受Ba含量控制。当x=0.6时，材料的Tc（max）达到98 K，达到了单层铜氧化物超导体的Tc记录值，高于具有最佳有序顶氧原子的Sr_2CuO_3 + δ的Tc =95 K。Sr_（2-x）CuO_（3+）δ中存在Sr位无序，这可能导致T_c降低。结果表明，另一种效应超过了无序效应，这与面内Cu-O键长的增加或由于具有较大阳离子尺寸的Ba取代而延长的顶-O距离有关。本实验表明，优化Cu-O平面外的局部几何结构可以显著提高铜氧化物超导体的Tc。
A series of new Sr2-xBaxCuO3+delta (0 < x < 0.6) superconductors were prepared using high-pressure and high-temperature synthesis. A Rietveld refinement based on powder x-ray diffraction confirms that the superconductors crystallize in the K2NiF4-type structure of a space group I4/mmm similar to that of La2CuO4 but with partially occupied apical oxygen sites. It is found that the superconducting transition temperature T-c of this Ba substituted Sr2CuO3+delta superconductor with constant carrier-doping level, i.e., constant delta is controlled not only by order/disorder of apical-O atoms but also by Ba content. T-c(max)=98 K is achieved in the material with x=0.6 that reaches the record value of T-c among the single-layer copper oxide superconductors and is higher than T-c=95 K of Sr2CuO3+delta with optimally ordered apical-O atoms. There is Sr-site disorder in Sr2-xBaxCuO3+delta which might lead to a reduction in T-c. The result indicates that another effect surpasses the disorder effect that is related either to the increased in-plane Cu-O bond length or to elongated apical-O distance due to Ba substitution with larger cation size. The present experiment demonstrates that the optimization of local geometry out of the Cu-O plane can dramatically enhance T-c in the cuprate superconductors.