Department of Chemistry, Lomonosov Moscow State University , 119991 Moscow, Russia.
Inorg Chem. 2013 Dec 16;52(24):14419-27. doi: 10.1021/ic402710r. Epub 2013 Nov 27.
Superconducting (SC) and non-superconducting (non-SC)Rb(x)Fe(2-y)Se2 crystals were grown using the "self-flux" technique in order to assign the microstructural changes to the onset of superconductivity in complex iron selenides. The crystals were thoroughly characterized by magnetic susceptibility and transport measurements as well as powder X-ray diffraction. Special attention was paid to the comparison of the microstructure of the crystals with and without the superconducting transition by means of transmission electron microscopy (TEM). It is shown that the alternation of ordered and disordered regions on the sample surface and along the c-axis is characteristic for both SC and non-SC materials and therefore does not necessarily represent a trigger of superconductivity. Three types of electron diffraction patterns were found for the superconducting Rb(x)Fe(2-y)Se2 sample, of which one is observed for the first time and originates from alkali metal ordering. Moreover, for the superconducting Rb(x)Fe(2-y)Se2 material a monoclinic distortion with β ∼ 87° was observed, leading to the space group I2/m. This monoclinic distortion seems to be an attribute of the superconducting material only, whereas in the non-superconducting sample the orthogonality of the crystallographic axes is preserved.
采用“自熔”技术生长超导（SC）和非超导（non-SC）Rb(x)Fe(2-y)Se2 晶体，以便将微结构变化归因于复杂铁硒化物的超导起始。通过磁敏和输运测量以及粉末 X 射线衍射对晶体进行了彻底的表征。特别关注通过透射电子显微镜（TEM）比较具有和不具有超导转变的晶体的微观结构。结果表明，在样品表面和 c 轴上有序和无序区域的交替对于 SC 和非 SC 材料都是特征性的，因此不一定代表超导的触发因素。对于超导 Rb(x)Fe(2-y)Se2 样品，发现了三种类型的电子衍射图案，其中一种是首次观察到的，源自碱金属有序。此外，对于超导 Rb(x)Fe(2-y)Se2 材料，观察到β≈87°的单斜畸变，导致空间群 I2/m。这种单斜畸变似乎是超导材料的属性，而在非超导样品中，晶轴的正交性得以保留。
