DOE OSTI2020
Ba3GeO5 crystallizes in the trigonal R3m space group. The structure is three-dimensional. there are three inequivalent Ba2+ sites. In the first Ba2+ site, Ba2+ is bonded in a distorted hexagonal planar geometry to six O2- atoms. There are a spread of Ba–O bond distances ranging from 2.72–2.83 Å. In the second Ba2+ site, Ba2+ is bonded to six O2- atoms to form distorted BaO6 octahedra that share corners with two equivalent BaO6 octahedra, a cornercorner with one BaO6 pentagonal pyramid, corners with four GeO4 tetrahedra, edges with two equivalent BaO6 pentagonal pyramids, and faces with two equivalent BaO6 octahedra. The corner-sharing octahedral tilt angles are 81°. There are a spread of Ba–O bond distances ranging from 2.71–2.81 Å. In the third Ba2+ site, Ba2+ is bonded to six O2- atoms to form distorted BaO6 pentagonal pyramids that share a cornercorner with one BaO6 octahedra, corners with two equivalent BaO6 pentagonal pyramids, corners with four GeO4 tetrahedra, edges with two equivalent BaO6 octahedra, and faces with two equivalent BaO6 pentagonal pyramids. The corner-sharing octahedral tilt angles are 1°. There are a spread of Ba–O bond distances ranging from 2.70–2.78 Å. There are three inequivalent Ge4+ sites. In the first Ge4+ site, Ge4+ is bonded to four O2- atoms to form GeO4 tetrahedra that share corners with six equivalent BaO6 octahedra and corners with three equivalent BaO6 pentagonal pyramids. The corner-sharing octahedral tilt angles are 54°. There is three shorter (1.79 Å) and one longer (1.80 Å) Ge–O bond length. In the second Ge4+ site, Ge4+ is bonded to four O2- atoms to form GeO4 tetrahedra that share corners with three equivalent BaO6 octahedra and corners with three equivalent BaO6 pentagonal pyramids. The corner-sharing octahedral tilt angles are 62°. There is three shorter (1.79 Å) and one longer (1.80 Å) Ge–O bond length. In the third Ge4+ site, Ge4+ is bonded to four O2- atoms to form GeO4 tetrahedra that share corners with three equivalent BaO6 octahedra and corners with six equivalent BaO6 pentagonal pyramids. The corner-sharing octahedral tilt angles are 55°. There is one shorter (1.78 Å) and three longer (1.79 Å) Ge–O bond length. There are nine inequivalent O2- sites. In the first O2- site, O2- is bonded to three equivalent Ba2+ and one Ge4+ atom to form distorted corner-sharing OBa3Ge tetrahedra. The corner-sharing octahedra tilt angles range from 11–63°. In the second O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to three Ba2+ and one Ge4+ atom. In the third O2- site, O2- is bonded in a rectangular see-saw-like geometry to three Ba2+ and one Ge4+ atom. In the fourth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to three Ba2+ and one Ge4+ atom. In the fifth O2- site, O2- is bonded to six Ba2+ atoms to form OBa6 octahedra that share corners with three equivalent OBa6 octahedra, corners with three equivalent OBa3Ge tetrahedra, and a faceface with one OBa6 octahedra. The corner-sharing octahedral tilt angles are 2°. In the sixth O2- site, O2- is bonded to six Ba2+ atoms to form OBa6 octahedra that share corners with six OBa3Ge tetrahedra and faces with two OBa6 octahedra. In the seventh O2- site, O2- is bonded to six Ba2+ atoms to form OBa6 octahedra that share corners with three equivalent OBa6 octahedra, corners with three equivalent OBa3Ge tetrahedra, and a faceface with one OBa6 octahedra. The corner-sharing octahedral tilt angles are 2°. In the eighth O2- site, O2- is bonded to three equivalent Ba2+ and one Ge4+ atom to form distorted corner-sharing OBa3Ge tetrahedra. The corner-sharing octahedra tilt angles range from 8–65°. In the ninth O2- site, O2- is bonded in a 1-coordinate geometry to three equivalent Ba2+ and one Ge4+ atom.