Wang ZC1, He CY1, Wu SQ1, Tang ZT1, Liu Y1, Ablimit A1, Feng CM1, Cao GH1,2.
J Am Chem Soc. 2016 Jun 29;138(25):7856-9. doi: 10.1021/jacs.6b04538. Epub 2016 Jun 21.We report the synthesis, crystal structure, and physical properties of a quinary iron arsenide fluoride, KCa2Fe4As4F2. The new compound crystallizes in a body-centered tetragonal lattice (space group I4/mmm, a = 3.8684(2) Å, c = 31.007(1) Å, Z = 2) that contains double Fe2As2 conducting layers separated by insulating Ca2F2 layers. Our measurements of electrical resistivity, direct-current magnetic susceptibility, and heat capacity demonstrate bulk superconductivity at 33 K in KCa2Fe4As4F2.