DOE OSTI2020
Sr5Al2Sb6 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are three inequivalent Sr2+ sites. In the first Sr2+ site, Sr2+ is bonded in a 7-coordinate geometry to seven Sb+2.67- atoms. There are a spread of Sr–Sb bond distances ranging from 3.41–3.85 Å. In the second Sr2+ site, Sr2+ is bonded to seven Sb+2.67- atoms to form distorted SrSb7 pentagonal bipyramids that share corners with two equivalent SrSb6 octahedra, corners with six AlSb4 tetrahedra, edges with two equivalent SrSb7 pentagonal bipyramids, an edgeedge with one AlSb4 tetrahedra, and faces with four equivalent SrSb6 octahedra. The corner-sharing octahedral tilt angles are 45°. There are a spread of Sr–Sb bond distances ranging from 3.21–3.81 Å. In the third Sr2+ site, Sr2+ is bonded to six Sb+2.67- atoms to form SrSb6 octahedra that share corners with two equivalent SrSb6 octahedra, a cornercorner with one SrSb7 pentagonal bipyramid, corners with two equivalent AlSb4 tetrahedra, edges with two equivalent SrSb6 octahedra, edges with three AlSb4 tetrahedra, and faces with two equivalent SrSb7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 41°. There are a spread of Sr–Sb bond distances ranging from 3.25–3.48 Å. There are two inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to four Sb+2.67- atoms to form AlSb4 tetrahedra that share corners with four equivalent SrSb6 octahedra, corners with three equivalent SrSb7 pentagonal bipyramids, a cornercorner with one AlSb4 tetrahedra, edges with two equivalent SrSb6 octahedra, an edgeedge with one SrSb7 pentagonal bipyramid, and an edgeedge with one AlSb4 tetrahedra. The corner-sharing octahedra tilt angles range from 49–68°. There are a spread of Al–Sb bond distances ranging from 2.69–2.80 Å. In the second Al3+ site, Al3+ is bonded to four Sb+2.67- atoms to form AlSb4 tetrahedra that share corners with three equivalent SrSb7 pentagonal bipyramids, a cornercorner with one AlSb4 tetrahedra, edges with four equivalent SrSb6 octahedra, and an edgeedge with one AlSb4 tetrahedra. There are a spread of Al–Sb bond distances ranging from 2.69–2.76 Å. There are five inequivalent Sb+2.67- sites. In the first Sb+2.67- site, Sb+2.67- is bonded in a 7-coordinate geometry to five Sr2+ and two Al3+ atoms. In the second Sb+2.67- site, Sb+2.67- is bonded in a 1-coordinate geometry to six Sr2+, one Al3+, and one Sb+2.67- atom. The Sb–Sb bond length is 2.95 Å. In the third Sb+2.67- site, Sb+2.67- is bonded in a 7-coordinate geometry to six Sr2+ and one Al3+ atom. In the fourth Sb+2.67- site, Sb+2.67- is bonded in a 6-coordinate geometry to four Sr2+ and two Al3+ atoms. In the fifth Sb+2.67- site, Sb+2.67- is bonded in a 9-coordinate geometry to eight Sr2+ and one Sb+2.67- atom.