DOE OSTI2020
Sr2CaI6 is zeta iron carbide-derived structured and crystallizes in the trigonal P321 space group. The structure is three-dimensional. there are two inequivalent Sr2+ sites. In the first Sr2+ site, Sr2+ is bonded to six I1- atoms to form SrI6 octahedra that share corners with four equivalent CaI6 octahedra, corners with six equivalent SrI6 octahedra, and an edgeedge with one CaI6 octahedra. The corner-sharing octahedra tilt angles range from 51–53°. There are a spread of Sr–I bond distances ranging from 3.31–3.34 Å. In the second Sr2+ site, Sr2+ is bonded to six I1- atoms to form SrI6 octahedra that share corners with two equivalent CaI6 octahedra, corners with six equivalent SrI6 octahedra, and edges with two equivalent CaI6 octahedra. The corner-sharing octahedra tilt angles range from 51–56°. There are four shorter (3.30 Å) and two longer (3.31 Å) Sr–I bond lengths. There are two inequivalent Ca2+ sites. In the first Ca2+ site, Ca2+ is bonded to six I1- atoms to form CaI6 octahedra that share corners with six equivalent SrI6 octahedra and edges with three equivalent SrI6 octahedra. The corner-sharing octahedra tilt angles range from 51–53°. There are three shorter (3.15 Å) and three longer (3.16 Å) Ca–I bond lengths. In the second Ca2+ site, Ca2+ is bonded to six equivalent I1- atoms to form CaI6 octahedra that share corners with six equivalent SrI6 octahedra and edges with three equivalent SrI6 octahedra. The corner-sharing octahedral tilt angles are 56°. All Ca–I bond lengths are 3.15 Å. There are three inequivalent I1- sites. In the first I1- site, I1- is bonded in a distorted trigonal planar geometry to two Sr2+ and one Ca2+ atom. In the second I1- site, I1- is bonded in a distorted trigonal planar geometry to two Sr2+ and one Ca2+ atom. In the third I1- site, I1- is bonded in a distorted trigonal planar geometry to two Sr2+ and one Ca2+ atom.