DOE OSTI2020
CaZr4O9 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. there are three inequivalent Ca2+ sites. In the first Ca2+ site, Ca2+ is bonded in a body-centered cubic geometry to eight O2- atoms. There are a spread of Ca–O bond distances ranging from 2.31–2.56 Å. In the second Ca2+ site, Ca2+ is bonded in a body-centered cubic geometry to eight O2- atoms. There are a spread of Ca–O bond distances ranging from 2.34–2.63 Å. In the third Ca2+ site, Ca2+ is bonded in a distorted body-centered cubic geometry to eight O2- atoms. There are a spread of Ca–O bond distances ranging from 2.35–2.70 Å. There are nine inequivalent Zr4+ sites. In the first Zr4+ site, Zr4+ is bonded to seven O2- atoms to form distorted ZrO7 pentagonal bipyramids that share a cornercorner with one ZrO6 octahedra, corners with two ZrO7 pentagonal bipyramids, an edgeedge with one ZrO6 octahedra, and edges with four ZrO7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 50°. There are a spread of Zr–O bond distances ranging from 2.07–2.27 Å. In the second Zr4+ site, Zr4+ is bonded to seven O2- atoms to form distorted ZrO7 pentagonal bipyramids that share a cornercorner with one ZrO6 octahedra, corners with two ZrO7 pentagonal bipyramids, and edges with four ZrO7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 54°. There are a spread of Zr–O bond distances ranging from 2.12–2.32 Å. In the third Zr4+ site, Zr4+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Zr–O bond distances ranging from 2.09–2.20 Å. In the fourth Zr4+ site, Zr4+ is bonded to six O2- atoms to form ZrO6 octahedra that share a cornercorner with one ZrO6 octahedra, corners with five ZrO7 pentagonal bipyramids, and an edgeedge with one ZrO7 pentagonal bipyramid. The corner-sharing octahedral tilt angles are 50°. There are a spread of Zr–O bond distances ranging from 2.04–2.19 Å. In the fifth Zr4+ site, Zr4+ is bonded to six O2- atoms to form ZrO6 octahedra that share corners with two equivalent ZrO6 octahedra, corners with four ZrO7 pentagonal bipyramids, and edges with two equivalent ZrO7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 50°. There are a spread of Zr–O bond distances ranging from 2.08–2.14 Å. In the sixth Zr4+ site, Zr4+ is bonded to seven O2- atoms to form distorted ZrO7 pentagonal bipyramids that share a cornercorner with one ZrO6 octahedra, corners with two ZrO7 pentagonal bipyramids, an edgeedge with one ZrO6 octahedra, and edges with three ZrO7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 48°. There are a spread of Zr–O bond distances ranging from 2.10–2.35 Å. In the seventh Zr4+ site, Zr4+ is bonded in a distorted body-centered cubic geometry to eight O2- atoms. There are a spread of Zr–O bond distances ranging from 2.10–2.59 Å. In the eighth Zr4+ site, Zr4+ is bonded to seven O2- atoms to form distorted ZrO7 pentagonal bipyramids that share corners with two ZrO6 octahedra, a cornercorner with one ZrO7 pentagonal bipyramid, and edges with four ZrO7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 44°. There are a spread of Zr–O bond distances ranging from 2.14–2.27 Å. In the ninth Zr4+ site, Zr4+ is bonded to seven O2- atoms to form distorted ZrO7 pentagonal bipyramids that share corners with two ZrO6 octahedra, a cornercorner with one ZrO7 pentagonal bipyramid, and edges with five ZrO7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 40–47°. There are a spread of Zr–O bond distances ranging from 2.15–2.32 Å. There are eighteen inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three Zr4+ atoms. In the second O2- site, O2- is bonded to four Zr4+ atoms to form a mixture of distorted edge and corner-sharing OZr4 tetrahedra. In the third O2- site, O2- is bonded in a 4-coordinate geometry to one Ca2+ and three Zr4+ atoms. In the fourth O2- site, O2- is bonded to one Ca2+ and three Zr4+ atoms to form a mixture of distorted edge and corner-sharing OCaZr3 tetrahedra. In the fifth O2- site, O2- is bonded to four Zr4+ atoms to form a mixture of distorted edge and corner-sharing OZr4 tetrahedra. In the sixth O2- site, O2- is bonded to two equivalent Ca2+ and two Zr4+ atoms to form a mixture of distorted edge and corner-sharing OCa2Zr2 tetrahedra. In the seventh O2- site, O2- is bonded to one Ca2+ and three Zr4+ atoms to form OCaZr3 tetrahedra that share corners with eleven OCaZr3 tetrahedra and an edgeedge with one OCa2Zr2 tetrahedra. In the eighth O2- site, O2- is bonded to two Ca2+ and two Zr4+ atoms to form distorted OCa2Zr2 tetrahedra that share corners with eight OZr4 tetrahedra and edges with four OCaZr3 tetrahedra. In the ninth O2- site, O2- is bonded to one Ca2+ and three Zr4+ atoms to form a mixture of edge and corner-sharing OCaZr3 tetrahedra. In the tenth O2- site, O2- is bonded to one Ca2+ and three Zr4+ atoms to form distorted OCaZr3 tetrahedra that share corners with ten OCaZr3 tetrahedra and edges with three OZr4 tetrahedra. In the eleventh O2- site, O2- is bonded to two Ca2+ and two Zr4+ atoms to form distorted OCa2Zr2 tetrahedra that share corners with nine OCaZr3 tetrahedra and edges with three OCa2Zr2 tetrahedra. In the twelfth O2- site, O2- is bonded in a 4-coordinate geometry to one Ca2+ and three Zr4+ atoms. In the thirteenth O2- site, O2- is bonded to one Ca2+ and three Zr4+ atoms to form a mixture of edge and corner-sharing OCaZr3 tetrahedra. In the fourteenth O2- site, O2- is bonded to one Ca2+ and three Zr4+ atoms to form a mixture of distorted edge and corner-sharing OCaZr3 tetrahedra. In the fifteenth O2- site, O2- is bonded to one Ca2+ and three Zr4+ atoms to form a mixture of edge and corner-sharing OCaZr3 tetrahedra. In the sixteenth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three Zr4+ atoms. In the seventeenth O2- site, O2- is bonded in a 4-coordinate geometry to four Zr4+ atoms. In the eighteenth O2- site, O2- is bonded in a 4-coordinate geometry to one Ca2+ and three Zr4+ atoms.