| Sumario: | 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 SrAFeAs (A = Rb, Cs), which can be regarded as hybrid phases between AeFeAs (Ae = Ca, Sr) and AFeAs. Unlike solid solutions such as (Ba1-xKx)FeAs and (SrNa)FeAs, 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 FeAs layers in the c-axis direction in AeAFeAs (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.
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