Materials Data on Ca2AlP2O9 by Materials Project
Ca2AlP2O9 crystallizes in the monoclinic P2_1/m space group. The structure is three-dimensional. there are two inequivalent Ca sites. In the first Ca site, Ca is bonded to six O atoms to form distorted CaO6 octahedra that share corners with two equivalent AlO6 octahedra and corners with six PO4 tetrahedra. The corner-sharing octahedral tilt angles are 61°. There are a spread of Ca–O bond distances ranging from 2.32–2.54 Å. In the second Ca site, Ca is bonded in a 6-coordinate geometry to six O atoms. There are a spread of Ca–O bond distances ranging from 2.31–2.55 Å. Al is bonded to six O atoms to form AlO6 octahedra that share corners with two equivalent CaO6 octahedra, corners with four PO4 tetrahedra, and edges with two equivalent AlO6 octahedra. The corner-sharing octahedral tilt angles are 61°. There are a spread of Al–O bond distances ranging from 1.82–1.98 Å. There are two inequivalent P sites. In the first P site, P is bonded to four O atoms to form PO4 tetrahedra that share corners with two equivalent AlO6 octahedra and corners with three equivalent CaO6 octahedra. The corner-sharing octahedra tilt angles range from 46–62°. There are a spread of P–O bond distances ranging from 1.53–1.60 Å. In the second P site, P is bonded to four O atoms to form PO4 tetrahedra that share corners with two equivalent AlO6 octahedra and corners with three equivalent CaO6 octahedra. The corner-sharing octahedra tilt angles range from 56–65°. There are a spread of P–O bond distances ranging from 1.52–1.58 Å. There are seven inequivalent O sites. In the first O site, O is bonded in a distorted trigonal planar geometry to one Ca, one Al, and one P atom. In the second O site, O is bonded in a 2-coordinate geometry to one Ca and one P atom. In the third O site, O is bonded in a linear geometry to one Ca and one P atom. In the fourth O site, O is bonded in a 1-coordinate geometry to three Ca and one P atom. In the fifth O site, O is bonded in a bent 120 degrees geometry to one Ca and one P atom. In the sixth O site, O is bonded in a distorted T-shaped geometry to two equivalent Al and one P atom. In the seventh O site, O is bonded in a distorted trigonal planar geometry to one Ca and two equivalent Al atoms.