DOE OSTI2020
(Fe2As2)(Sr4MgTiO6) crystallizes in the tetragonal P4mm space group. The structure is three-dimensional. there are four inequivalent Sr2+ sites. In the first Sr2+ site, Sr2+ is bonded in a 4-coordinate geometry to four equivalent As3- and four equivalent O2- atoms. All Sr–As bond lengths are 3.46 Å. All Sr–O bond lengths are 2.49 Å. In the second Sr2+ site, Sr2+ is bonded in a 8-coordinate geometry to four equivalent As3- and four equivalent O2- atoms. All Sr–As bond lengths are 3.22 Å. All Sr–O bond lengths are 2.60 Å. In the third Sr2+ site, Sr2+ is bonded in a 9-coordinate geometry to nine O2- atoms. There are a spread of Sr–O bond distances ranging from 2.66–3.06 Å. In the fourth Sr2+ site, Sr2+ is bonded in a 1-coordinate geometry to nine O2- atoms. There are a spread of Sr–O bond distances ranging from 2.24–3.01 Å. Mg2+ is bonded to five O2- atoms to form corner-sharing MgO5 square pyramids. There are four shorter (2.04 Å) and one longer (2.09 Å) Mg–O bond lengths. Ti4+ is bonded to five O2- atoms to form corner-sharing TiO5 square pyramids. There is one shorter (1.80 Å) and four longer (2.03 Å) Ti–O bond length. Fe2+ is bonded to four As3- atoms to form a mixture of edge and corner-sharing FeAs4 tetrahedra. There are two shorter (2.57 Å) and two longer (2.63 Å) Fe–As bond lengths. There are two inequivalent As3- sites. In the first As3- site, As3- is bonded in a 8-coordinate geometry to four equivalent Sr2+ and four equivalent Fe2+ atoms. In the second As3- site, As3- is bonded in a 8-coordinate geometry to four equivalent Sr2+ and four equivalent Fe2+ atoms. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded to four Sr2+ and two equivalent Mg2+ atoms to form a mixture of distorted edge, face, and corner-sharing OSr4Mg2 octahedra. The corner-sharing octahedral tilt angles are 19°. In the second O2- site, O2- is bonded in a 6-coordinate geometry to four Sr2+ and two equivalent Ti4+ atoms. In the third O2- site, O2- is bonded in a distorted linear geometry to five Sr2+ and one Mg2+ atom. In the fourth O2- site, O2- is bonded in a distorted single-bond geometry to five Sr2+ and one Ti4+ atom.