Superconductivity in a new iron pnictide oxide (Fe2As2)(Sr4(Mg, Ti)2O6)

We have discovered a new iron pnictide oxide superconductor (Fe2As2)(Sr-4(Mg, Ti)(2)O-6). This material is isostructural with (Fe2As2)(Sr4M2O6) (M = Sc, Cr, V), which were found in previous studies. The structure of this compound is tetragonal with a space group of P4/nmm and consists of the anti-fluorite type FeAs layer and perovskite-type block layer. The lattice constants are a = 3.935 angstrom and c = 15.952 angstrom for (Fe2As2)(Sr4MgTiO6). Bulk superconductivity with a T-c(onset) of similar to 26 K was observed for a partially Co-substituted sample. Moreover, Co-free and Ti-rich samples exhibited higher T(c(onset))s above 35 K, which were further enhanced by applying high pressures up to similar to 43 K.