Materials Data on BaAl5O9 by Materials Project
BaAl5O9 crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Ba is bonded in a 9-coordinate geometry to nine O atoms. There are six shorter (2.79 Å) and three longer (3.30 Å) Ba–O bond lengths. There are two inequivalent Al sites. In the first Al site, Al is bonded to six O atoms to form AlO6 octahedra that share corners with four equivalent AlO4 tetrahedra and edges with four equivalent AlO6 octahedra. There is two shorter (1.88 Å) and four longer (1.95 Å) Al–O bond length. In the second Al site, Al is bonded to four O atoms to form AlO4 tetrahedra that share corners with six equivalent AlO6 octahedra and a cornercorner with one AlO4 tetrahedra. The corner-sharing octahedral tilt angles are 57°. There is one shorter (1.75 Å) and three longer (1.78 Å) Al–O bond length. There are three inequivalent O sites. In the first O site, O is bonded in a linear geometry to three equivalent Ba and two equivalent Al atoms. In the second O site, O is bonded in a 4-coordinate geometry to one Ba and three Al atoms. In the third O site, O is bonded in a distorted trigonal non-coplanar geometry to three equivalent Al atoms.