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首页> 外文期刊>Physical review >Phase relations in K_xFe_(2-y)Se_2 and the structure of superconducting K_xFe_2Se_2 via high-resolution synchrotron diffraction
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Phase relations in K_xFe_(2-y)Se_2 and the structure of superconducting K_xFe_2Se_2 via high-resolution synchrotron diffraction

机译：K_xFe_（2-y）Se_2中的相位关系和高分辨率同步加速器衍射的超导K_xFe_2Se_2的结构

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Superconductivity in iron selenides has experienced a rapid growth, but not without major inconsistencies in the reported properties. For alkali-intercalated iron selenides, even the-structure of the superconducting phase is a subject of debate, in part because the onset of superconductivity is affected much more delicately by stoichiometry and preparation than in cuprate or pnictide superconductors. If high-quality, pure, superconducting intercalated iron selenides are ever to be made, the intertwined physics and chemistry must be explained by systematic studies of how these materials form and by and identifying the many coexisting phases. To that end, we prepared pure K_2Fe_4Se_5 powder and superconductors in the K_xFe_(2-y)Se_2 system, and examined differences in their structures by high-resolution synchrotron and single-crystal x-ray diffraction. We found four distinct phases: semiconducting K_2Fe_4Se_5, a metallic superconducting phase K_xFe_2Se_2 with x ranging from 0.38 to 0.58, the phase KFe_(1.6)Se_2 with full K occupancy and no Fe vacancy ordering, and a oxidized phase K_(0.51(5))Fe_(0.70(2))Se that forms the PbCIF structure upon exposure to moisture. We find that the vacancy-ordered phase K_2Fe_4Se_5 does not become superconducting by doping, but the distinct iron-rich minority phase K_xFe_2Se_2 precipitates from single crystals upon cooling from above the vacancy ordering temperature. This coexistence of separate metallic and semiconducting phases explains a broad maximum in resistivity around 100 K. Further studies to understand the solubility of excess Fe in the K_xFe_(2-y)Se_2 structure will shed light on the maximum fraction of superconducting K_xFe_2Se_2 that can be obtained by solid state synthesis.
机译：硒化铁中的超导性经历了快速的增长，但是在所报告的特性中并非没有重大矛盾。对于碱插层的硒化铁，甚至是超导相的结构也是一个争论的话题，部分原因是化学计量和制备对超导电性的影响要比对铜酸盐或p化物超导体更为微妙。如果要生产高质量，纯净，超导的插层硒化铁，则必须通过对这些材料的形成方式的系统研究以及确定并存的许多相来解释相互交织的物理化学。为此，我们在K_xFe_（2-y）Se_2系统中制备了纯K_2Fe_4Se_5粉末和超导体，并通过高分辨率同步加速器和单晶x射线衍射检查了它们的结构差异。我们发现了四个不同的相：半导体K_2Fe_4Se_5，金属超导相K_xFe_2Se_2（x的范围从0.38到0.58），相KFe_（1.6）Se_2具有完全的K占据并且没有Fe空位有序，以及氧化相K_（0.51（5）） Fe_（0.70（2））Se在暴露于湿气时形成PbCIF结构。我们发现，空位有序相K_2Fe_4Se_5不会因掺杂而超导，但是从空位有序温度以上冷却后，单晶中会析出明显的富铁少数相K_xFe_2Se_2。分离的金属相和半导体相的共存解释了大约100 K的电阻率的最大值。进一步的研究以了解过量的Fe在K_xFe_（2-y）Se_2结构中的溶解度将阐明超导K_xFe_2Se_2的最大分数。通过固态合成获得。

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  • 来源
    《Physical review》 |2012年第18期|184511.1-184511.12|共12页
  • 作者

    Daniel P. Shoemaker; Duck Young Chung; Helmut Claus; Melanie C. Francisco; Sevda Avci; Anna Llobet; Mercouri G. Kanatzidis;

  • 作者单位

    Materials Science Division, Argonne National Laboratory, Argonne, Illinois, 60439, USA;

    Materials Science Division, Argonne National Laboratory, Argonne, Illinois, 60439, USA;

    Materials Science Division, Argonne National Laboratory, Argonne, Illinois, 60439, USA;

    Materials Science Division, Argonne National Laboratory, Argonne, Illinois, 60439, USA;

    Materials Science Division, Argonne National Laboratory, Argonne, Illinois, 60439, USA;

    Los Alamos National Laboratory, Lujan Neutron Scattering Center, MS H805, Los Alamos, New Mexico 87545, USA;

    Materials Science Division, Argonne National Laboratory, Argonne, Illinois, 60439, USA,Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States;

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