DOE OSTI2020
Ga4B2O9 crystallizes in the monoclinic Cm space group. The structure is three-dimensional. there are six inequivalent Ga3+ sites. In the first Ga3+ site, Ga3+ is bonded to six O2- atoms to form GaO6 octahedra that share a cornercorner with one BO4 tetrahedra, corners with two GaO4 tetrahedra, a cornercorner with one GaO5 trigonal bipyramid, edges with two equivalent GaO6 octahedra, and an edgeedge with one GaO5 trigonal bipyramid. There are a spread of Ga–O bond distances ranging from 1.86–2.10 Å. In the second Ga3+ site, Ga3+ is bonded to five O2- atoms to form GaO5 trigonal bipyramids that share corners with two equivalent GaO6 octahedra, corners with two GaO4 tetrahedra, edges with two equivalent GaO6 octahedra, and an edgeedge with one GaO5 trigonal bipyramid. The corner-sharing octahedral tilt angles are 49°. There are a spread of Ga–O bond distances ranging from 1.86–2.15 Å. In the third Ga3+ site, Ga3+ is bonded to four O2- atoms to form distorted GaO4 tetrahedra that share corners with four GaO6 octahedra, corners with two equivalent BO4 tetrahedra, and corners with two GaO5 trigonal bipyramids. The corner-sharing octahedra tilt angles range from 52–75°. There are a spread of Ga–O bond distances ranging from 1.83–1.89 Å. In the fourth Ga3+ site, Ga3+ is bonded to six O2- atoms to form GaO6 octahedra that share a cornercorner with one BO4 tetrahedra, corners with two GaO4 tetrahedra, a cornercorner with one GaO5 trigonal bipyramid, edges with two equivalent GaO6 octahedra, and an edgeedge with one GaO5 trigonal bipyramid. There are a spread of Ga–O bond distances ranging from 1.87–2.12 Å. In the fifth Ga3+ site, Ga3+ is bonded to five O2- atoms to form GaO5 trigonal bipyramids that share corners with two equivalent GaO6 octahedra, a cornercorner with one GaO4 tetrahedra, edges with two equivalent GaO6 octahedra, and an edgeedge with one GaO5 trigonal bipyramid. The corner-sharing octahedral tilt angles are 52°. There are a spread of Ga–O bond distances ranging from 1.85–2.07 Å. In the sixth Ga3+ site, Ga3+ is bonded to four O2- atoms to form GaO4 tetrahedra that share corners with four GaO6 octahedra, a cornercorner with one BO4 tetrahedra, and a cornercorner with one GaO5 trigonal bipyramid. The corner-sharing octahedra tilt angles range from 67–71°. There is one shorter (1.79 Å) and three longer (1.93 Å) Ga–O bond length. There are four inequivalent B3+ sites. In the first B3+ site, B3+ is bonded in a trigonal planar geometry to three O2- atoms. There is one shorter (1.37 Å) and two longer (1.41 Å) B–O bond length. In the second B3+ site, B3+ is bonded in a trigonal planar geometry to three O2- atoms. All B–O bond lengths are 1.39 Å. In the third B3+ site, B3+ is bonded in a trigonal planar geometry to three O2- atoms. There is one shorter (1.37 Å) and two longer (1.39 Å) B–O bond length. In the fourth B3+ site, B3+ is bonded to four O2- atoms to form BO4 tetrahedra that share corners with four GaO6 octahedra and corners with three GaO4 tetrahedra. The corner-sharing octahedra tilt angles range from 52–59°. There are a spread of B–O bond distances ranging from 1.44–1.54 Å. There are fourteen inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to two Ga3+ and one B3+ atom. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to two Ga3+ and one B3+ atom. In the third O2- site, O2- is bonded in a trigonal pyramidal geometry to four Ga3+ atoms. In the fourth O2- site, O2- is bonded in a trigonal planar geometry to three Ga3+ atoms. In the fifth O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Ga3+ and one B3+ atom. In the sixth O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Ga3+ and one B3+ atom. In the seventh O2- site, O2- is bonded in a trigonal planar geometry to two Ga3+ and one B3+ atom. In the eighth O2- site, O2- is bonded in a 3-coordinate geometry to two Ga3+ and one B3+ atom. In the ninth O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Ga3+ and one B3+ atom. In the tenth O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Ga3+ and one B3+ atom. In the eleventh O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to four Ga3+ atoms. In the twelfth O2- site, O2- is bonded in a distorted trigonal planar geometry to three Ga3+ atoms. In the thirteenth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three Ga3+ atoms. In the fourteenth O2- site, O2- is bonded in a bent 120 degrees geometry to one Ga3+ and one B3+ atom.