Materials Data on Ba2Ta2O7 by Materials Project
Ba2Ta2O7 crystallizes in the orthorhombic Imma space group. The structure is three-dimensional. there are two inequivalent Ba2+ sites. In the first Ba2+ site, Ba2+ is bonded to eight O2- atoms to form distorted BaO8 hexagonal bipyramids that share corners with two equivalent BaO8 hexagonal bipyramids, corners with two equivalent TaO6 octahedra, edges with four equivalent BaO8 hexagonal bipyramids, and edges with six TaO6 octahedra. The corner-sharing octahedral tilt angles are 53°. There are a spread of Ba–O bond distances ranging from 2.54–3.02 Å. In the second Ba2+ site, Ba2+ is bonded to eight O2- atoms to form distorted BaO8 hexagonal bipyramids that share edges with six BaO8 hexagonal bipyramids and edges with six TaO6 octahedra. There are four shorter (2.61 Å) and four longer (3.07 Å) Ba–O bond lengths. There are two inequivalent Ta5+ sites. In the first Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with six TaO6 octahedra and edges with six BaO8 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 35–39°. There are four shorter (2.02 Å) and two longer (2.05 Å) Ta–O bond lengths. In the second Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with two equivalent BaO8 hexagonal bipyramids, corners with four equivalent TaO6 octahedra, and edges with six BaO8 hexagonal bipyramids. The corner-sharing octahedral tilt angles are 35°. There are two shorter (1.96 Å) and four longer (2.06 Å) Ta–O bond lengths. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a 2-coordinate geometry to two Ba2+ and two Ta5+ atoms. In the second O2- site, O2- is bonded in a 4-coordinate geometry to three Ba2+ and one Ta5+ atom. In the third O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two equivalent Ba2+ and two equivalent Ta5+ atoms.