Materials Data on KErP2O9 by Materials Project
KErP2O9 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. K is bonded in a 9-coordinate geometry to nine O atoms. There are a spread of K–O bond distances ranging from 2.71–3.22 Å. Er is bonded to seven O atoms to form distorted ErO7 pentagonal bipyramids that share corners with six PO4 tetrahedra. There are a spread of Er–O bond distances ranging from 2.25–2.56 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 ErO7 pentagonal bipyramids and a cornercorner with one PO4 tetrahedra. There are a spread of P–O bond distances ranging from 1.52–1.64 Å. In the second P site, P is bonded to four O atoms to form PO4 tetrahedra that share corners with three equivalent ErO7 pentagonal bipyramids and a cornercorner with one PO4 tetrahedra. There is three shorter (1.53 Å) and one longer (1.65 Å) P–O bond length. There are nine inequivalent O sites. In the first O site, O is bonded in a 2-coordinate geometry to one K, one Er, and one P atom. In the second O site, O is bonded in a 3-coordinate geometry to one K, one Er, and one P atom. In the third O site, O is bonded in a 3-coordinate geometry to one K, one Er, and one P atom. In the fourth O site, O is bonded in a 1-coordinate geometry to one K and one O atom. The O–O bond length is 2.02 Å. In the fifth O site, O is bonded in a 1-coordinate geometry to one K, one Er, and one P atom. In the sixth O site, O is bonded in a 1-coordinate geometry to one K, one Er, and one O atom. In the seventh O site, O is bonded in a 3-coordinate geometry to one K, one Er, and one P atom. In the eighth O site, O is bonded in a 2-coordinate geometry to one K, one Er, and one P atom. In the ninth O site, O is bonded in a distorted bent 120 degrees geometry to one K and two P atoms.