New-Structure-Type Fe-Based Superconductors: CaAFe4As4 (A = K, Rb, Cs) and SrAFe4As4 (A = Rb, Cs)

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• 作者：Akira Iyo ; Kenji Kawashima ; Tatsuya Kinjo ; Taichiro Nishio ; Shigeyuki Ishida ; Hiroshi Fujihisa ; Yoshito Gotoh ; Kunihiro Kihou ; Hiroshi Eisaki ; Yoshiyuki Yoshida
• 刊名：Journal of the American Chemical Society
• 出版年：2016
• 出版时间：March 16, 2016
• 年：2016
• 卷：138
• 期：10
• 页码：3410-3415
• 全文大小：470K
• ISSN：1520-5126

文摘

Fe-based superconductors have attracted research interest because of their rich structural variety, which is due to their layered crystal structures. Here we report the new-structure-type Fe-based superconductors CaAFe₄As₄ (A = K, Rb, Cs) and SrAFe₄As₄ (A = Rb, Cs), which can be regarded as hybrid phases between AeFe₂As₂ (Ae = Ca, Sr) and AFe₂As₂. Unlike solid solutions such as (Ba_1–xK_x)Fe₂As₂ and (Sr_1–xNa_x)Fe₂As₂, Ae and A do not occupy crystallographically equivalent sites because of the large differences between their ionic radii. Rather, the Ae and A layers are inserted alternately between the Fe₂As₂ layers in the c-axis direction in AeAFe₄As₄ (AeA1144). The ordering of the Ae and A layers causes a change in the space group from I4/mmm to P4/mmm, which is clearly apparent in powder X-ray diffraction patterns. AeA1144 is the first known structure of this type among not only Fe-based superconductors but also other materials. AeA1144 is formed as a line compound, and therefore, each AeA1144 has its own superconducting transition temperature of approximately 31–36 K.