DOE OSTI2020
BaCa2I6 is zeta iron carbide-derived structured and crystallizes in the monoclinic C2 space group. The structure is three-dimensional. there are two inequivalent Ba2+ sites. In the first Ba2+ site, Ba2+ is bonded to six I1- atoms to form BaI6 octahedra that share corners with six CaI6 octahedra and edges with three CaI6 octahedra. The corner-sharing octahedra tilt angles range from 56–58°. There are three shorter (3.45 Å) and three longer (3.46 Å) Ba–I bond lengths. In the second Ba2+ site, Ba2+ is bonded to six I1- atoms to form BaI6 octahedra that share corners with six CaI6 octahedra and edges with three CaI6 octahedra. The corner-sharing octahedral tilt angles are 60°. All Ba–I bond lengths are 3.46 Å. There are four inequivalent Ca2+ sites. In the first Ca2+ site, Ca2+ is bonded to six I1- atoms to form CaI6 octahedra that share corners with four equivalent BaI6 octahedra, corners with six CaI6 octahedra, and an edgeedge with one BaI6 octahedra. The corner-sharing octahedra tilt angles range from 43–58°. There are a spread of Ca–I bond distances ranging from 3.19–3.21 Å. In the second Ca2+ site, Ca2+ is bonded to six I1- atoms to form CaI6 octahedra that share corners with two equivalent BaI6 octahedra, corners with six CaI6 octahedra, and edges with two equivalent BaI6 octahedra. The corner-sharing octahedra tilt angles range from 43–60°. There are a spread of Ca–I bond distances ranging from 3.18–3.20 Å. In the third Ca2+ site, Ca2+ is bonded to six I1- atoms to form CaI6 octahedra that share corners with two equivalent BaI6 octahedra, corners with six CaI6 octahedra, and edges with two equivalent BaI6 octahedra. The corner-sharing octahedra tilt angles range from 43–60°. There are a spread of Ca–I bond distances ranging from 3.18–3.20 Å. In the fourth Ca2+ site, Ca2+ is bonded to six I1- atoms to form CaI6 octahedra that share corners with four equivalent BaI6 octahedra, corners with six CaI6 octahedra, and an edgeedge with one BaI6 octahedra. The corner-sharing octahedra tilt angles range from 43–58°. There are two shorter (3.19 Å) and four longer (3.20 Å) Ca–I bond lengths. There are nine inequivalent I1- sites. In the first I1- site, I1- is bonded in a distorted trigonal planar geometry to one Ba2+ and two Ca2+ atoms. In the second I1- site, I1- is bonded in a distorted trigonal planar geometry to one Ba2+ and two Ca2+ atoms. In the third I1- site, I1- is bonded in a distorted trigonal planar geometry to one Ba2+ and two Ca2+ atoms. In the fourth I1- site, I1- is bonded in a distorted trigonal planar geometry to one Ba2+ and two Ca2+ atoms. In the fifth I1- site, I1- is bonded in a distorted trigonal planar geometry to one Ba2+ and two Ca2+ atoms. In the sixth I1- site, I1- is bonded in a distorted trigonal planar geometry to one Ba2+ and two Ca2+ atoms. In the seventh I1- site, I1- is bonded in a distorted trigonal planar geometry to one Ba2+ and two Ca2+ atoms. In the eighth I1- site, I1- is bonded in a distorted trigonal planar geometry to one Ba2+ and two Ca2+ atoms. In the ninth I1- site, I1- is bonded in a distorted trigonal planar geometry to one Ba2+ and two Ca2+ atoms.