Materials Data on HfP2O9 by Materials Project
(Hf(PO4)2)2O2 crystallizes in the monoclinic P2_1/c space group. The structure is two-dimensional and consists of four water molecules and two Hf(PO4)2 sheets oriented in the (0, 0, 1) direction. In each Hf(PO4)2 sheet, Hf is bonded to six O atoms to form HfO6 octahedra that share corners with six PO4 tetrahedra. There are a spread of Hf–O bond distances ranging from 2.05–2.07 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 three equivalent HfO6 octahedra. The corner-sharing octahedra tilt angles range from 11–33°. There are a spread of P–O bond distances ranging from 1.53–1.56 Å. In the second P site, P is bonded to four O atoms to form PO4 tetrahedra that share corners with three equivalent HfO6 octahedra. The corner-sharing octahedra tilt angles range from 17–34°. There is three shorter (1.54 Å) and one longer (1.57 Å) P–O bond length. There are eight inequivalent O sites. In the first O site, O is bonded in a bent 150 degrees geometry to one Hf and one P atom. In the second O site, O is bonded in a single-bond geometry to one P atom. In the third O site, O is bonded in a bent 150 degrees geometry to one Hf and one P atom. In the fourth O site, O is bonded in a linear geometry to one Hf and one P atom. In the fifth O site, O is bonded in a bent 150 degrees geometry to one Hf and one P atom. In the sixth O site, O is bonded in a bent 150 degrees geometry to one Hf and one P atom. In the seventh O site, O is bonded in a single-bond geometry to one P atom. In the eighth O site, O is bonded in a linear geometry to one Hf and one P atom.