  We have discovered a new iron pnictide oxide superconductor
(Fe2As2)(Sr4(Mg,Ti)2O6). This material is isostructual 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 A and c = 15.952 A for (Fe2As2)(Sr4MgTiO6). Bulk
superconductivity with Tc(onset) of ~26 K was observed for a partially Co
substituted sample. Moreover, Co-free and Ti-rich samples exhibited higher
Tc(onset)'s above 35 K, which were further enhanced by applying high pressures
up to ~43 K.
