DOE OSTI2020
Sr2Ti5Al17O38 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. Sr is bonded to twelve O atoms to form distorted SrO12 cuboctahedra that share corners with two equivalent SrO12 cuboctahedra, corners with five AlO6 octahedra, a cornercorner with one AlO4 tetrahedra, edges with three AlO6 octahedra, an edgeedge with one AlO4 tetrahedra, faces with two equivalent SrO12 cuboctahedra, a faceface with one AlO6 octahedra, and faces with five TiO6 octahedra. The corner-sharing octahedra tilt angles range from 45–53°. There are a spread of Sr–O bond distances ranging from 2.64–3.04 Å. There are three inequivalent Ti sites. In the first Ti site, Ti is bonded to six O atoms to form distorted TiO6 octahedra that share corners with two equivalent AlO6 octahedra, corners with four equivalent TiO6 octahedra, edges with three AlO6 octahedra, and faces with four equivalent SrO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 13–18°. There are a spread of Ti–O bond distances ranging from 1.85–2.18 Å. In the second Ti site, Ti is bonded to six O atoms to form TiO6 octahedra that share a cornercorner with one TiO6 octahedra, corners with four AlO6 octahedra, corners with three equivalent AlO4 tetrahedra, and edges with three AlO6 octahedra. The corner-sharing octahedra tilt angles range from 46–52°. There are a spread of Ti–O bond distances ranging from 1.86–2.15 Å. In the third Ti site, Ti is bonded to six O atoms to form distorted TiO6 octahedra that share corners with three TiO6 octahedra, corners with four AlO6 octahedra, a cornercorner with one AlO4 tetrahedra, an edgeedge with one AlO6 octahedra, and faces with three equivalent SrO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 13–55°. There are a spread of Ti–O bond distances ranging from 1.88–2.24 Å. There are nine inequivalent Al sites. In the first Al site, Al is bonded to six O atoms to form AlO6 octahedra that share corners with two TiO6 octahedra, corners with two AlO6 octahedra, corners with three AlO4 tetrahedra, edges with four AlO6 octahedra, and a faceface with one SrO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 14–52°. There are a spread of Al–O bond distances ranging from 1.83–2.06 Å. In the second Al site, Al is bonded to six O atoms to form AlO6 octahedra that share corners with three equivalent SrO12 cuboctahedra, a cornercorner with one TiO6 octahedra, corners with two AlO6 octahedra, corners with two AlO4 tetrahedra, edges with two TiO6 octahedra, and edges with three AlO6 octahedra. The corner-sharing octahedral tilt angles are 52°. There are a spread of Al–O bond distances ranging from 1.84–2.09 Å. In the third Al site, Al is bonded to six O atoms to form AlO6 octahedra that share corners with two equivalent SrO12 cuboctahedra, corners with four equivalent AlO4 tetrahedra, an edgeedge with one TiO6 octahedra, and edges with six AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.90–1.92 Å. In the fourth Al site, Al is bonded to four O atoms to form AlO4 tetrahedra that share a cornercorner with one SrO12 cuboctahedra, a cornercorner with one TiO6 octahedra, corners with eight AlO6 octahedra, and an edgeedge with one SrO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 48–62°. There are a spread of Al–O bond distances ranging from 1.76–1.82 Å. In the fifth Al site, Al is bonded to four O atoms to form AlO4 tetrahedra that share corners with three equivalent TiO6 octahedra and corners with eight AlO6 octahedra. The corner-sharing octahedra tilt angles range from 54–63°. There are a spread of Al–O bond distances ranging from 1.77–1.83 Å. In the sixth Al site, Al is bonded to six O atoms to form AlO6 octahedra that share corners with two equivalent TiO6 octahedra, corners with two AlO6 octahedra, corners with two equivalent AlO4 tetrahedra, an edgeedge with one SrO12 cuboctahedra, an edgeedge with one TiO6 octahedra, and edges with three AlO6 octahedra. The corner-sharing octahedra tilt angles range from 21–52°. There are a spread of Al–O bond distances ranging from 1.89–1.98 Å. In the seventh Al site, Al is bonded to six O atoms to form AlO6 octahedra that share a cornercorner with one TiO6 octahedra, corners with three AlO6 octahedra, a cornercorner with one AlO4 tetrahedra, an edgeedge with one SrO12 cuboctahedra, an edgeedge with one TiO6 octahedra, and edges with four AlO6 octahedra. The corner-sharing octahedra tilt angles range from 21–56°. There are a spread of Al–O bond distances ranging from 1.84–2.04 Å. In the eighth Al site, Al is bonded to six O atoms to form AlO6 octahedra that share a cornercorner with one TiO6 octahedra, corners with two AlO6 octahedra, corners with two equivalent AlO4 tetrahedra, an edgeedge with one SrO12 cuboctahedra, an edgeedge with one TiO6 octahedra, and edges with four AlO6 octahedra. The corner-sharing octahedra tilt angles range from 51–55°. There are a spread of Al–O bond distances ranging from 1.84–2.04 Å. In the ninth Al site, Al is bonded to six O atoms to form AlO6 octahedra that share a cornercorner with one SrO12 cuboctahedra, a cornercorner with one AlO6 octahedra, corners with two equivalent TiO6 octahedra, corners with four AlO4 tetrahedra, and edges with four AlO6 octahedra. The corner-sharing octahedra tilt angles range from 49–56°. There are a spread of Al–O bond distances ranging from 1.85–2.01 Å. There are nineteen inequivalent O sites. In the first O site, O is bonded in a distorted trigonal planar geometry to one Ti and two Al atoms. In the second O site, O is bonded in a 2-coordinate geometry to two equivalent Sr, one Ti, and one Al atom. In the third O site, O is bonded to four Al atoms to form distorted OAl4 tetrahedra that share a cornercorner with one OTiAl3 trigonal pyramid and an edgeedge with one OAl4 trigonal pyramid. In the fourth O site, O is bonded in a distorted trigonal planar geometry to two Ti and one Al atom. In the fifth O site, O is bonded in a 4-coordinate geometry to one Sr and three Al atoms. In the sixth O site, O is bonded in a 4-coordinate geometry to one Sr, one Ti, and two Al atoms. In the seventh O site, O is bonded to one Ti and three Al atoms to form distorted corner-sharing OTiAl3 trigonal pyramids. In the eighth O site, O is bonded in a trigonal planar geometry to one Ti and two Al atoms. In the ninth O site, O is bonded in a 2-coordinate geometry to three equivalent Sr and two Ti atoms. In the tenth O site, O is bonded in a trigonal planar geometry to one Ti and two Al atoms. In the eleventh O site, O is bonded in a rectangular see-saw-like geometry to four Al atoms. In the twelfth O site, O is bonded in a 4-coordinate geometry to one Sr, one Ti, and two Al atoms. In the thirteenth O site, O is bonded to four Al atoms to form a mixture of distorted corner and edge-sharing OAl4 trigonal pyramids. In the fourteenth O site, O is bonded in a 3-coordinate geometry to two equivalent Sr, two Ti, and one Al atom. In the fifteenth O site, O is bonded in a trigonal planar geometry to three Al atoms. In the sixteenth O site, O is bonded in a 4-coordinate geometry to one Sr, one Ti, and three Al atoms. In the seventeenth O site, O is bonded in a rectangular see-saw-like geometry to four Al atoms. In the eighteenth O site, O is bonded in a 4-coordinate geometry to one Sr and three Al atoms. In the nineteenth O site, O is bonded in a distorted rectangular see-saw-like geometry to one Ti and three Al atoms.