DOE OSTI2020
Ba4Cr13O28 crystallizes in the monoclinic Pm space group. The structure is three-dimensional. there are four inequivalent Ba2+ sites. In the first Ba2+ site, Ba2+ is bonded to twelve O2- atoms to form BaO12 cuboctahedra that share corners with six BaO12 cuboctahedra, corners with two equivalent CrO4 tetrahedra, edges with three CrO6 octahedra, edges with three CrO4 tetrahedra, faces with three BaO12 cuboctahedra, and faces with four CrO6 octahedra. There are a spread of Ba–O bond distances ranging from 2.78–2.99 Å. In the second Ba2+ site, Ba2+ is bonded to twelve O2- atoms to form BaO12 cuboctahedra that share corners with six BaO12 cuboctahedra, a cornercorner with one CrO4 tetrahedra, edges with three CrO6 octahedra, edges with three CrO4 tetrahedra, faces with three BaO12 cuboctahedra, and faces with four CrO6 octahedra. There are a spread of Ba–O bond distances ranging from 2.87–3.08 Å. In the third Ba2+ site, Ba2+ is bonded to twelve O2- atoms to form distorted BaO12 cuboctahedra that share corners with six BaO12 cuboctahedra, corners with three CrO4 tetrahedra, edges with three CrO6 octahedra, edges with two equivalent CrO4 tetrahedra, faces with three BaO12 cuboctahedra, and faces with four CrO6 octahedra. There are a spread of Ba–O bond distances ranging from 2.72–3.16 Å. In the fourth Ba2+ site, Ba2+ is bonded to twelve O2- atoms to form BaO12 cuboctahedra that share corners with six BaO12 cuboctahedra, corners with three CrO4 tetrahedra, edges with three CrO6 octahedra, an edgeedge with one CrO4 tetrahedra, faces with three BaO12 cuboctahedra, and faces with four CrO6 octahedra. There are a spread of Ba–O bond distances ranging from 2.81–3.19 Å. There are eleven inequivalent Cr+3.69+ sites. In the first Cr+3.69+ site, Cr+3.69+ is bonded to six O2- atoms to form CrO6 octahedra that share corners with six CrO6 octahedra, a cornercorner with one CrO4 tetrahedra, and faces with four BaO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 49–54°. There are a spread of Cr–O bond distances ranging from 1.73–2.18 Å. In the second Cr+3.69+ site, Cr+3.69+ is bonded to six O2- atoms to form CrO6 octahedra that share corners with six CrO6 octahedra, corners with two equivalent CrO4 tetrahedra, and faces with four BaO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 50–53°. There are a spread of Cr–O bond distances ranging from 1.75–2.10 Å. In the third Cr+3.69+ site, Cr+3.69+ is bonded to six O2- atoms to form CrO6 octahedra that share corners with six CrO6 octahedra, corners with three CrO4 tetrahedra, and faces with four BaO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 51–53°. There are a spread of Cr–O bond distances ranging from 2.00–2.08 Å. In the fourth Cr+3.69+ site, Cr+3.69+ is bonded to six O2- atoms to form CrO6 octahedra that share corners with six CrO6 octahedra, corners with three CrO4 tetrahedra, and faces with four BaO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 52–53°. There are a spread of Cr–O bond distances ranging from 2.01–2.09 Å. In the fifth Cr+3.69+ site, Cr+3.69+ is bonded to six O2- atoms to form CrO6 octahedra that share corners with four CrO6 octahedra, a cornercorner with one CrO4 tetrahedra, edges with two BaO12 cuboctahedra, and edges with four CrO6 octahedra. The corner-sharing octahedra tilt angles range from 50–53°. There are a spread of Cr–O bond distances ranging from 1.93–2.02 Å. In the sixth Cr+3.69+ site, Cr+3.69+ is bonded to six O2- atoms to form CrO6 octahedra that share corners with four CrO6 octahedra, corners with two CrO4 tetrahedra, edges with two BaO12 cuboctahedra, and edges with four CrO6 octahedra. The corner-sharing octahedra tilt angles range from 49–53°. There are a spread of Cr–O bond distances ranging from 1.97–2.00 Å. In the seventh Cr+3.69+ site, Cr+3.69+ is bonded to six O2- atoms to form CrO6 octahedra that share corners with four CrO6 octahedra, a cornercorner with one CrO4 tetrahedra, edges with two BaO12 cuboctahedra, and edges with four CrO6 octahedra. The corner-sharing octahedra tilt angles range from 51–54°. There are a spread of Cr–O bond distances ranging from 1.92–2.04 Å. In the eighth Cr+3.69+ site, Cr+3.69+ is bonded to six O2- atoms to form CrO6 octahedra that share corners with four CrO6 octahedra, corners with two CrO4 tetrahedra, edges with two BaO12 cuboctahedra, and edges with four CrO6 octahedra. The corner-sharing octahedra tilt angles range from 50–53°. There are a spread of Cr–O bond distances ranging from 1.98–2.00 Å. In the ninth Cr+3.69+ site, Cr+3.69+ is bonded to four O2- atoms to form CrO4 tetrahedra that share corners with three BaO12 cuboctahedra, corners with six CrO6 octahedra, and edges with three BaO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 41–59°. There are a spread of Cr–O bond distances ranging from 1.76–1.88 Å. In the tenth Cr+3.69+ site, Cr+3.69+ is bonded to four O2- atoms to form CrO4 tetrahedra that share corners with three BaO12 cuboctahedra, corners with six CrO6 octahedra, and edges with three BaO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 49–58°. There is three shorter (1.78 Å) and one longer (1.90 Å) Cr–O bond length. In the eleventh Cr+3.69+ site, Cr+3.69+ is bonded to four O2- atoms to form CrO4 tetrahedra that share corners with three BaO12 cuboctahedra, corners with six CrO6 octahedra, and edges with three BaO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 50–59°. There is three shorter (1.78 Å) and one longer (1.88 Å) Cr–O bond length. There are twenty inequivalent O2- sites. In the first O2- site, O2- is bonded in a 2-coordinate geometry to three Ba2+ and two Cr+3.69+ atoms. In the second O2- site, O2- is bonded in a 2-coordinate geometry to three Ba2+ and two Cr+3.69+ atoms. In the third O2- site, O2- is bonded in a 2-coordinate geometry to three Ba2+ and two Cr+3.69+ atoms. In the fourth O2- site, O2- is bonded in a 2-coordinate geometry to three Ba2+ and two Cr+3.69+ atoms. In the fifth O2- site, O2- is bonded in a distorted single-bond geometry to three Ba2+ and one Cr+3.69+ atom. In the sixth O2- site, O2- is bonded in a 2-coordinate geometry to three Ba2+ and two Cr+3.69+ atoms. In the seventh O2- site, O2- is bonded in a 2-coordinate geometry to three Ba2+ and two Cr+3.69+ atoms. In the eighth O2- site, O2- is bonded in a distorted single-bond geometry to three Ba2+ and one Cr+3.69+ atom. In the ninth O2- site, O2- is bonded in a 4-coordinate geometry to one Ba2+ and three Cr+3.69+ atoms. In the tenth O2- site, O2- is bonded in a 3-coordinate geometry to one Ba2+ and three Cr+3.69+ atoms. In the eleventh O2- site, O2- is bonded in a 3-coordinate geometry to one Ba2+ and three Cr+3.69+ atoms. In the twelfth O2- site, O2- is bonded in a 3-coordinate geometry to one Ba2+ and three Cr+3.69+ atoms. In the thirteenth O2- site, O2- is bonded in a 3-coordinate geometry to one Ba2+ and three Cr+3.69+ atoms. In the fourteenth O2- site, O2- is bonded in a 3-coordinate geometry to one Ba2+ and three Cr+3.69+ atoms. In the fifteenth O2- site, O2- is bonded in a 3-coordinate geometry to one Ba2+ and three Cr+3.69+ atoms. In the sixteenth O2- site, O2- is bonded in a 3-coordinate geometry to one Ba2+ and three Cr+3.69+ atoms. In the seventeenth O2- site, O2- is bonded in a distorted T-shaped geometry to three Cr+3.69+ atoms. In the eighteenth O2- site, O2- is bonded to four Cr+3.69+ atoms to form distorted corner-sharing OCr4 trigonal pyramids. In the nineteenth O2- site, O2- is bonded to four Cr+3.69+ atoms to form distorted corner-sharing OCr4 trigonal pyramids. In the twentieth O2- site, O2- is bonded to four Cr+3.69+ atoms to form distorted corner-sharing OCr4 trigonal pyramids.