铁基K0.8Fe2-ySe2体系的单晶生长与结构研究

本文报道了采用自助溶剂法对不同组分K0.8Fe2-ySe2单晶生长和结构研究的实验结果.X-射线衍射XRD(Cu靶和同步辐射)结构分析表明样品中存在两套衍射峰(分别对应相1和相2),相1能够用ThCr2Si2结构,空间群I4/mmm(No.139)指标化,对应超导相.而相2能够用单一米勒指数(0 0l)标定,可能对应一个新的物相.相2的存在能够在不同组分的KxFe2-ySe2单晶样品中很好的重复.利用高分辨透射电子显微镜(TEM)研究了K0.8Fe2Se2样品的"结构相分离"特征,结果表明样品中存在明显的位错缺陷,可能与两相结构的竞争有关.对K0.8Fe2Se2单晶样品直流磁化测量表明相2可能为弱铁磁性,从而引起高温Tp～125K的ZFC与FC磁性反常.

SINGLE CRYSTAL GROWTH AND STRUCTURE STUDY OF K0.8Fe2-ySe2 IRON-SELENIDES

In this paper,we reported the results of single crystal growth and structure study of various stoichiometric K0.8Fe2-ySe2 iron-selenides,which were grown by self-flux method.Two phases corresponding to phase 1 and phase 2 were detected by performing both Cu target and synchrotron x-ray diffractions,in which phase 1 could be indexed to tetragonal ThCr2Si2-like structure with space group I4/mmm(No.139) and be related to superconductivity.However,the series reflections of phase 2 could also belong to a single Millér index(0 0 l),indicating a new structural phase.The phase 2 could be reproduced in various stoichiometric K0.8Fe2-ySe2 samples.The dislocation defects were observed in K0.8Fe2Se2 crystal in TEM measurement,as may be connected with the competition between two phases.The measurement of temperature dependent magnetization on K0.8Fe2Se2 crystal showed that phase 2 might be weak ferromagnetism and be responsible for the high temperature magnetic abnormality at Tp~125K.