DOE OSTI2020
SrCa(CuO2)2 crystallizes in the orthorhombic Amm2 space group. The structure is three-dimensional. Sr2+ is bonded to seven O2- atoms to form distorted SrO7 pentagonal bipyramids that share corners with four equivalent SrO7 pentagonal bipyramids, edges with two equivalent SrO7 pentagonal bipyramids, edges with four equivalent CaO7 pentagonal bipyramids, and faces with two equivalent SrO7 pentagonal bipyramids. There are a spread of Sr–O bond distances ranging from 2.42–2.65 Å. Ca2+ is bonded to seven O2- atoms to form distorted CaO7 pentagonal bipyramids that share corners with four equivalent CaO7 pentagonal bipyramids, edges with two equivalent CaO7 pentagonal bipyramids, edges with four equivalent SrO7 pentagonal bipyramids, and faces with two equivalent CaO7 pentagonal bipyramids. There are a spread of Ca–O bond distances ranging from 2.38–2.64 Å. There are two inequivalent Cu2+ sites. In the first Cu2+ site, Cu2+ is bonded in a square co-planar geometry to four O2- atoms. There are a spread of Cu–O bond distances ranging from 1.88–1.97 Å. In the second Cu2+ site, Cu2+ is bonded in a square co-planar geometry to four O2- atoms. There are a spread of Cu–O bond distances ranging from 1.95–1.97 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded to two equivalent Sr2+ and three Cu2+ atoms to form OSr2Cu3 trigonal bipyramids that share corners with seven OSrCa4Cu octahedra, corners with four equivalent OSr2Cu3 trigonal bipyramids, edges with two equivalent OCa2Cu3 trigonal bipyramids, and faces with two equivalent OSr4CaCu octahedra. The corner-sharing octahedra tilt angles range from 0–59°. In the second O2- site, O2- is bonded to two equivalent Ca2+ and three Cu2+ atoms to form OCa2Cu3 trigonal bipyramids that share corners with seven OSrCa4Cu octahedra, corners with four equivalent OCa2Cu3 trigonal bipyramids, edges with two equivalent OSr2Cu3 trigonal bipyramids, and faces with two equivalent OSrCa4Cu octahedra. The corner-sharing octahedra tilt angles range from 0–59°. In the third O2- site, O2- is bonded to one Sr2+, four equivalent Ca2+, and one Cu2+ atom to form distorted OSrCa4Cu octahedra that share corners with four equivalent OSrCa4Cu octahedra, corners with seven OSr2Cu3 trigonal bipyramids, edges with eight OSrCa4Cu octahedra, and faces with two equivalent OCa2Cu3 trigonal bipyramids. The corner-sharing octahedral tilt angles are 8°. In the fourth O2- site, O2- is bonded to four equivalent Sr2+, one Ca2+, and one Cu2+ atom to form distorted OSr4CaCu octahedra that share corners with four equivalent OSr4CaCu octahedra, corners with seven OSr2Cu3 trigonal bipyramids, edges with eight OSrCa4Cu octahedra, and faces with two equivalent OSr2Cu3 trigonal bipyramids. The corner-sharing octahedral tilt angles are 10°.