Materials Data on BaSrTa2O7 by Materials Project
BaSrTa2O7 crystallizes in the orthorhombic Immm space group. The structure is three-dimensional. Ba2+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ba–O bond distances ranging from 2.74–3.07 Å. There are two inequivalent Sr2+ sites. In the first Sr2+ site, Sr2+ is bonded to twelve O2- atoms to form distorted SrO12 cuboctahedra that share corners with four equivalent SrO12 cuboctahedra, faces with four SrO12 cuboctahedra, and faces with eight equivalent TaO6 octahedra. There are a spread of Sr–O bond distances ranging from 2.62–3.07 Å. In the second Sr2+ site, Sr2+ is bonded to twelve O2- atoms to form distorted SrO12 cuboctahedra that share corners with four equivalent SrO12 cuboctahedra, faces with four SrO12 cuboctahedra, and faces with eight equivalent TaO6 octahedra. There are a spread of Sr–O bond distances ranging from 2.59–3.04 Å. Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with five equivalent TaO6 octahedra and faces with four SrO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 12–27°. There are a spread of Ta–O bond distances ranging from 1.88–2.13 Å. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Sr2+ and two equivalent Ta5+ atoms. In the second O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to two Sr2+ and two equivalent Ta5+ atoms. In the third O2- site, O2- is bonded to three equivalent Ba2+ and one Ta5+ atom to form a mixture of distorted corner and edge-sharing OBa3Ta tetrahedra. In the fourth O2- site, O2- is bonded in a 4-coordinate geometry to four Sr2+ and two equivalent Ta5+ atoms. In the fifth O2- site, O2- is bonded in a distorted linear geometry to one Ba2+, two equivalent Sr2+, and two equivalent Ta5+ atoms.