DOE OSTI2020
Ca3Ru2O7 crystallizes in the orthorhombic Cmc2_1 space group. The structure is three-dimensional. there are two inequivalent Ca2+ sites. In the first Ca2+ site, Ca2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Ca–O bond distances ranging from 2.30–2.53 Å. In the second Ca2+ site, Ca2+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Ca–O bond distances ranging from 2.35–2.74 Å. Ru4+ is bonded to six O2- atoms to form corner-sharing RuO6 octahedra. The corner-sharing octahedra tilt angles range from 29–32°. There are a spread of Ru–O bond distances ranging from 2.01–2.05 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a 5-coordinate geometry to three Ca2+ and two equivalent Ru4+ atoms. In the second O2- site, O2- is bonded to three Ca2+ and two equivalent Ru4+ atoms to form distorted OCa3Ru2 trigonal bipyramids that share corners with five OCa2Ru2 tetrahedra, corners with two equivalent OCa3Ru2 trigonal bipyramids, edges with three OCa2Ru2 tetrahedra, and edges with three equivalent OCa3Ru2 trigonal bipyramids. In the third O2- site, O2- is bonded to two equivalent Ca2+ and two equivalent Ru4+ atoms to form distorted OCa2Ru2 tetrahedra that share corners with four OCa2Ru2 tetrahedra, corners with eight equivalent OCa3Ru2 trigonal bipyramids, and edges with two equivalent OCa3Ru2 trigonal bipyramids. In the fourth O2- site, O2- is bonded to three equivalent Ca2+ and one Ru4+ atom to form distorted OCa3Ru tetrahedra that share corners with seven OCa2Ru2 tetrahedra, a cornercorner with one OCa3Ru2 trigonal bipyramid, and edges with two equivalent OCa3Ru2 trigonal bipyramids.