Structural Features of Layered Iron Pnictide Oxides (Fe2As2)(Sr4M2O6)

Structural features of newly found perovskite-based iron pnictide oxide system have been systematically studied. Compared to REFePnO system, perovskite-based system tend to have lower Pn-Fe-Pn angle and higher pnictogen height owing to low electronegativity of alkaline earth metal and small repulsive force between pnictogen and oxygen atoms. As-Fe-As angles of (Fe2As2)(Sr4Cr2O6), (Fe2As2)(Sr4V2O6) and (Fe2Pn2)(Sr4MgTiO6) are close to ideal tetrahedron and those pnictogen heights of about 1.40 A are close to NdFeAsO with optimized carrier concentration. These structural features of this system may leads to realization of high Tc superconductivity.