DOE OSTI2020
NiOCaO crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are four inequivalent Ca2+ sites. In the first Ca2+ site, Ca2+ is bonded to six O2- atoms to form distorted CaO6 octahedra that share corners with two equivalent CaO6 octahedra, corners with two NiO4 trigonal pyramids, edges with seven CaO6 octahedra, and an edgeedge with one NiO4 trigonal pyramid. The corner-sharing octahedral tilt angles are 1°. There are a spread of Ca–O bond distances ranging from 2.29–2.85 Å. In the second Ca2+ site, Ca2+ is bonded to six O2- atoms to form distorted CaO6 octahedra that share corners with two equivalent CaO6 octahedra, corners with two NiO4 trigonal pyramids, edges with seven CaO6 octahedra, and an edgeedge with one NiO4 trigonal pyramid. The corner-sharing octahedral tilt angles are 1°. There are a spread of Ca–O bond distances ranging from 2.29–2.85 Å. In the third Ca2+ site, Ca2+ is bonded to six O2- atoms to form CaO6 octahedra that share corners with two equivalent CaO6 octahedra, corners with two equivalent NiO4 trigonal pyramids, edges with seven CaO6 octahedra, and edges with three NiO4 trigonal pyramids. The corner-sharing octahedral tilt angles are 1°. There are a spread of Ca–O bond distances ranging from 2.29–2.42 Å. In the fourth Ca2+ site, Ca2+ is bonded to six O2- atoms to form CaO6 octahedra that share corners with two equivalent CaO6 octahedra, corners with two equivalent NiO4 trigonal pyramids, edges with seven CaO6 octahedra, and edges with three NiO4 trigonal pyramids. The corner-sharing octahedral tilt angles are 1°. There are a spread of Ca–O bond distances ranging from 2.29–2.42 Å. There are four inequivalent Ni2+ sites. In the first Ni2+ site, Ni2+ is bonded in a distorted square co-planar geometry to four O2- atoms. There are a spread of Ni–O bond distances ranging from 1.93–2.23 Å. In the second Ni2+ site, Ni2+ is bonded to four O2- atoms to form distorted NiO4 trigonal pyramids that share corners with four CaO6 octahedra, corners with two equivalent NiO4 trigonal pyramids, and edges with four CaO6 octahedra. The corner-sharing octahedra tilt angles range from 8–85°. There are a spread of Ni–O bond distances ranging from 1.98–2.11 Å. In the third Ni2+ site, Ni2+ is bonded to four O2- atoms to form distorted NiO4 trigonal pyramids that share corners with four CaO6 octahedra, corners with two equivalent NiO4 trigonal pyramids, and edges with four CaO6 octahedra. The corner-sharing octahedra tilt angles range from 8–85°. There are a spread of Ni–O bond distances ranging from 1.98–2.10 Å. In the fourth Ni2+ site, Ni2+ is bonded in a distorted square co-planar geometry to four O2- atoms. There are a spread of Ni–O bond distances ranging from 1.93–2.25 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded to one Ca2+ and three Ni2+ atoms to form distorted OCaNi3 tetrahedra that share corners with two OCa5Ni octahedra, corners with six OCa3Ni2 square pyramids, corners with two equivalent OCaNi3 tetrahedra, an edgeedge with one OCa5Ni octahedra, and an edgeedge with one OCa3Ni2 square pyramid. The corner-sharing octahedra tilt angles range from 11–85°. In the second O2- site, O2- is bonded to three Ca2+ and two equivalent Ni2+ atoms to form OCa3Ni2 square pyramids that share corners with two equivalent OCa5Ni octahedra, corners with three OCa3Ni2 square pyramids, corners with two equivalent OCaNi3 tetrahedra, edges with three OCa5Ni octahedra, and edges with four OCa3Ni2 square pyramids. The corner-sharing octahedral tilt angles are 9°. In the third O2- site, O2- is bonded to three Ca2+ and two equivalent Ni2+ atoms to form OCa3Ni2 square pyramids that share corners with two equivalent OCa5Ni octahedra, corners with three OCa3Ni2 square pyramids, corners with two equivalent OCaNi3 tetrahedra, edges with three OCa5Ni octahedra, and edges with four OCa3Ni2 square pyramids. The corner-sharing octahedral tilt angles are 9°. In the fourth O2- site, O2- is bonded to one Ca2+ and three Ni2+ atoms to form distorted OCaNi3 tetrahedra that share corners with two OCa5Ni octahedra, corners with six OCa3Ni2 square pyramids, corners with two equivalent OCaNi3 tetrahedra, an edgeedge with one OCa5Ni octahedra, and an edgeedge with one OCa3Ni2 square pyramid. The corner-sharing octahedra tilt angles range from 11–85°. In the fifth O2- site, O2- is bonded to three Ca2+ and two equivalent Ni2+ atoms to form distorted OCa3Ni2 square pyramids that share corners with two equivalent OCa5Ni octahedra, corners with three OCa3Ni2 square pyramids, corners with four OCaNi3 tetrahedra, edges with three OCa5Ni octahedra, edges with two equivalent OCa3Ni2 square pyramids, and an edgeedge with one OCaNi3 tetrahedra. The corner-sharing octahedral tilt angles are 13°. In the sixth O2- site, O2- is bonded to five Ca2+ and one Ni2+ atom to form distorted OCa5Ni octahedra that share corners with four OCa3Ni2 square pyramids, corners with two OCaNi3 tetrahedra, edges with four OCa5Ni octahedra, edges with six OCa3Ni2 square pyramids, and an edgeedge with one OCaNi3 tetrahedra. In the seventh O2- site, O2- is bonded to three Ca2+ and two equivalent Ni2+ atoms to form distorted OCa3Ni2 square pyramids that share corners with two equivalent OCa5Ni octahedra, corners with three OCa3Ni2 square pyramids, corners with four OCaNi3 tetrahedra, edges with three OCa5Ni octahedra, edges with two equivalent OCa3Ni2 square pyramids, and an edgeedge with one OCaNi3 tetrahedra. The corner-sharing octahedra tilt angles range from 12–13°. In the eighth O2- site, O2- is bonded to five Ca2+ and one Ni2+ atom to form distorted OCa5Ni octahedra that share corners with four OCa3Ni2 square pyramids, corners with two OCaNi3 tetrahedra, edges with four OCa5Ni octahedra, edges with six OCa3Ni2 square pyramids, and an edgeedge with one OCaNi3 tetrahedra.