Effect of the FeSe Precursor on the Superconductivity of K x Fe2− y Se 2
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Three single crystals of K x Fe2−y Se2 with nominal compositions of K0.8Fe2Se2 were prepared by self-flux method in one step or two steps, employing different FeSe precursors as raw materials. Depending on the heat treatment times of FeSe precursors, these three K x Fe2−y Se2 crystals are symbolized by KFeSe-0, KFeSe-1, and KFeSe-2, respectively. The onset superconducting transition temperature for KFeSe-1 and KFeSe-2 is around 44 K which is much higher than that of 34.8 K for KFeSe-0. According to the structural and transport properties, it is inferred that the higher-onset transition temperature at 44 K might be derived from another iron-rich K x Fe2−y Se2 phase. The employment of FeSe precursors makes it more difficult for K ions to intercalate into FeSe layers, inducing a phase separation and the formation of a second iron-rich phase.
KeywordsK0.8Fe2Se2 Superconductivity Iron-based superconductor Transport properties Magnetic properties
The authors are grateful for the financial support of the National Natural Science Foundation of China (Grant Nos. 11104224 and 11004162), the Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20110184120029), and the Fundamental Research Funds for the Central Universities (Grant No. 2682015ZT11, No. 2682015CX008, 2682016ZDPY10). Y.L. Chen and Yajing Cui are also grateful for the financial support of China Scholarship Council and Li Jinsheng scholarship of Superconductivity and New Energy R&D Center.
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