A new iron pnictide oxide (Fe2As2) (Ca5 (Mg, Ti)4Oy) and a new phase in the Fe―As―Ca―Mg―Ti―O system

A new layered iron arsenide oxide (Fe2As2)(Ca5(Mg, Ti)4Oy) and its structural derivative were found in the Fe?As?Ca?Mg?Ti?O system. The crystal structure of (Fe2As2)(Ca5(Mg, Ti)4Oy) is identical to that of (Fe2As2)(Ca5(Sc, Ti)4Oy), which was reported in our previous study. The lattice constants of this compound are a = 3.86(4)?? and c = 41.05(2)??. In addition, another phase with a thicker blocking layer was found. The structure of the compound was tentatively assigned through scanning transmission electron microscope observation as (Fe2As2)(Ca8(Mg, Ti)6Oy) with sextuple perovskite-type sheets divided by a rock salt layer. The interlayer Fe?Fe distance of this compound is ~ 30??. These compounds exhibited bulk superconductivity, as found from magnetization and resistivity measurements.