DOE OSTI2020
NaCaAlF6 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are two inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded in a 7-coordinate geometry to seven F1- atoms. There are a spread of Na–F bond distances ranging from 2.24–2.84 Å. In the second Na1+ site, Na1+ is bonded to six F1- atoms to form distorted NaF6 pentagonal pyramids that share corners with two AlF6 octahedra, corners with two equivalent CaF7 pentagonal bipyramids, edges with two equivalent AlF6 octahedra, an edgeedge with one CaF7 pentagonal bipyramid, and an edgeedge with one NaF6 pentagonal pyramid. The corner-sharing octahedra tilt angles range from 37–56°. There are a spread of Na–F bond distances ranging from 2.22–2.49 Å. There are two inequivalent Ca2+ sites. In the first Ca2+ site, Ca2+ is bonded to seven F1- atoms to form distorted CaF7 pentagonal bipyramids that share corners with three AlF6 octahedra, corners with four CaF7 pentagonal bipyramids, edges with two AlF6 octahedra, and an edgeedge with one NaF6 pentagonal pyramid. The corner-sharing octahedra tilt angles range from 35–48°. There are a spread of Ca–F bond distances ranging from 2.21–2.47 Å. In the second Ca2+ site, Ca2+ is bonded to seven F1- atoms to form distorted CaF7 pentagonal bipyramids that share corners with three AlF6 octahedra, corners with two equivalent CaF7 pentagonal bipyramids, corners with two equivalent NaF6 pentagonal pyramids, edges with two AlF6 octahedra, and an edgeedge with one CaF7 pentagonal bipyramid. The corner-sharing octahedra tilt angles range from 28–37°. There are a spread of Ca–F bond distances ranging from 2.26–2.52 Å. There are two inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to six F1- atoms to form AlF6 octahedra that share corners with three CaF7 pentagonal bipyramids, a cornercorner with one NaF6 pentagonal pyramid, and edges with two CaF7 pentagonal bipyramids. There are a spread of Al–F bond distances ranging from 1.78–1.87 Å. In the second Al3+ site, Al3+ is bonded to six F1- atoms to form AlF6 octahedra that share corners with three CaF7 pentagonal bipyramids, a cornercorner with one NaF6 pentagonal pyramid, edges with two CaF7 pentagonal bipyramids, and edges with two equivalent NaF6 pentagonal pyramids. There are a spread of Al–F bond distances ranging from 1.79–1.85 Å. There are twelve inequivalent F1- sites. In the first F1- site, F1- is bonded in a distorted tetrahedral geometry to two Na1+, one Ca2+, and one Al3+ atom. In the second F1- site, F1- is bonded in a 4-coordinate geometry to two Na1+, one Ca2+, and one Al3+ atom. In the third F1- site, F1- is bonded in a 1-coordinate geometry to two Ca2+ and one Al3+ atom. In the fourth F1- site, F1- is bonded in a 4-coordinate geometry to two Na1+, one Ca2+, and one Al3+ atom. In the fifth F1- site, F1- is bonded in a distorted trigonal planar geometry to two Ca2+ and one Al3+ atom. In the sixth F1- site, F1- is bonded in a 3-coordinate geometry to one Na1+, one Ca2+, and one Al3+ atom. In the seventh F1- site, F1- is bonded in a 2-coordinate geometry to one Na1+, one Ca2+, and one Al3+ atom. In the eighth F1- site, F1- is bonded in a 3-coordinate geometry to two equivalent Ca2+ and one Al3+ atom. In the ninth F1- site, F1- is bonded in a 3-coordinate geometry to one Na1+, one Ca2+, and one Al3+ atom. In the tenth F1- site, F1- is bonded in a 3-coordinate geometry to two equivalent Na1+ and one Al3+ atom. In the eleventh F1- site, F1- is bonded in a distorted trigonal planar geometry to two equivalent Na1+ and one Al3+ atom. In the twelfth F1- site, F1- is bonded in a 1-coordinate geometry to two equivalent Ca2+ and one Al3+ atom.