A number of iron-based superconductors have been discovered, 1-3 which include LaFeAsO (1111-type structure), 4 BaFe 2 As 2 (122-type), 5 LiFeAs (111-type), 6 and FeSe (11-type), 7 as well as compounds with complex oxide spacer layers [8][9][10][11] and arsenide spacer layers such as Ca 10 (Pt 4 As 8 )(Fe 2 As 2 ) 5 . [12][13][14][15][16][17] The maximum superconducting transition temperature T c is 55 K of the 1111-type structure. 18 In order to further increase T c , an exploration of novel structure types should be performed.Very recently, Katayama et al. 19 and Yakita et al. 20 have reported superconductivity in Ca 1−x La x FeAs 2 and Ca 1−x Pr x FeAs 2 , respectively, with a novel 112-type structure. Ca 1−x La x FeAs 2 crystalizes in a monoclinic structure with the space group P2 1 (No. 4) and consists of alternately stacked Fe 2 As 2 and arsenic zigzag bond layers. 19 Although pure CaFeAs 2 was not obtained, Katayama et al. found that the substitution of a small amount of La for Ca stabilizes the 112 phase and induces superconductivity at T c = 34 K for x = 0.16. Interestingly, Katayama et al. 19 suggested that the trace superconductivity of Ca 1−x La x FeAs 2 could exhibit T c = 45 K.In this paper, we report that a large increase in T c occurs with the phosphorus or antimony doping of Ca 1−x La x FeAs 2 . P-doped Ca 0.84 La 0.16 FeAs 2 and Sb-doped Ca 0.85 La 0.15 FeAs 2 exhibited T c values of 41 and 43 K, respectively, while P/Sbfree Ca 0.85 La 0.15 FeAs 2 exhibited T c = 35 K.Single crystals of Ca 1−x La x Fe(As 1−y Pn y ) 2 (Pn = P and Sb) were grown by heating a mixture of Ca, La, FeAs, As, P, and Sb powders. A stoichiometric amount of the mixture was placed in an aluminum crucible and sealed in an evacuated quartz tube. The preparation was carried out in a glove box filled with argon gas. Ampules were heated at 700 • C for 3 h, heated to 1100 • C at a rate of 46 • C/h, and cooled to 1050 • C at a rate of 1.25 • C/h, followed by furnace cooling. The obtained samples were characterized by powder Xray diffraction (XRD) analysis, performed using a Rigaku RINT-TTR III X-ray diffractometer with CuK α radiation. The Ca 1−x La x Fe(As 1−y Pn y ) 2 was obtained together with a powder mixture of LaAs, FeAs, FeAs 2 , and CaFe 2 As 2 . We separated platelike single crystals of the present system with typ-

We report the unprecedented square-planar coordination of iridium in the iron iridium arsenide Ca 10 (Ir 4 As 8 )(Fe 2 As 2 ) 5 . This material experiences superconductivity at 16 K. X-ray photoemission spectroscopy and first-principles band calculation suggest Ir(II) oxidation state, which yields electrically conductive Ir 4 As 8 layers. Such metallic spacer layers are thought to enhance the interlayer coupling of Fe 2 As 2 , in which superconductivity emerges, thus offering a way to control the superconducting transition temperature.

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Angle-resolved photoemission spectroscopy of Ca10(Ir4As8)(Fe2−xIrxAs2)5 shows that the Fe 3d electrons in the FeAs layer form the hole-like Fermi pocket at the zone center and the electron-like Fermi pockets at the zone corners as commonly seen in various Fe-based superconductors. The FeAs layer is heavily electron doped and has relatively good two dimensionality. On the other hand, the Ir 5d electrons are metallic and glassy probably due to atomic disorder related to the Ir 5d orbital instability. Ca10(Ir4As8)(Fe2−xIrxAs2)5 exhibits a unique electronic state where the Bloch electrons in the FeAs layer coexist with the glassy electrons in the Ir4As8 layer.