DOE OSTI2020
Dy4Al2O9 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are four inequivalent Dy3+ sites. In the first Dy3+ site, Dy3+ is bonded to six O2- atoms to form DyO6 octahedra that share corners with five AlO4 tetrahedra and edges with two equivalent DyO7 hexagonal pyramids. There are a spread of Dy–O bond distances ranging from 2.21–2.38 Å. In the second Dy3+ site, Dy3+ is bonded to seven O2- atoms to form distorted DyO7 hexagonal pyramids that share corners with three AlO4 tetrahedra, edges with two equivalent DyO6 octahedra, and edges with two AlO4 tetrahedra. There are a spread of Dy–O bond distances ranging from 2.26–2.51 Å. In the third Dy3+ site, Dy3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Dy–O bond distances ranging from 2.25–2.68 Å. In the fourth Dy3+ site, Dy3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Dy–O bond distances ranging from 2.26–2.79 Å. There are two inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share corners with two equivalent DyO7 hexagonal pyramids, corners with two equivalent DyO6 octahedra, a cornercorner with one AlO4 tetrahedra, and an edgeedge with one DyO7 hexagonal pyramid. The corner-sharing octahedra tilt angles range from 39–53°. There are a spread of Al–O bond distances ranging from 1.76–1.78 Å. In the second Al3+ site, Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share a cornercorner with one DyO7 hexagonal pyramid, corners with three equivalent DyO6 octahedra, a cornercorner with one AlO4 tetrahedra, and an edgeedge with one DyO7 hexagonal pyramid. The corner-sharing octahedra tilt angles range from 51–61°. There are a spread of Al–O bond distances ranging from 1.75–1.78 Å. There are nine inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to three Dy3+ and one Al3+ atom. In the second O2- site, O2- is bonded to four Dy3+ atoms to form ODy4 tetrahedra that share corners with five ODy3Al tetrahedra and edges with two ODy4 tetrahedra. In the third O2- site, O2- is bonded in a 4-coordinate geometry to three Dy3+ and one Al3+ atom. In the fourth O2- site, O2- is bonded to three Dy3+ and one Al3+ atom to form distorted ODy3Al tetrahedra that share corners with six ODy4 tetrahedra and an edgeedge with one ODy2Al2 tetrahedra. In the fifth O2- site, O2- is bonded to two Dy3+ and two Al3+ atoms to form distorted ODy2Al2 tetrahedra that share corners with three ODy4 tetrahedra and edges with two ODy3Al tetrahedra. In the sixth O2- site, O2- is bonded in a distorted trigonal planar geometry to two Dy3+ and one Al3+ atom. In the seventh O2- site, O2- is bonded in a 4-coordinate geometry to three Dy3+ and one Al3+ atom. In the eighth O2- site, O2- is bonded to four Dy3+ atoms to form a mixture of edge and corner-sharing ODy4 tetrahedra. In the ninth O2- site, O2- is bonded in a 4-coordinate geometry to three Dy3+ and one Al3+ atom.