DOE OSTI2020
FeP2O9 crystallizes in the monoclinic Cc space group. The structure is three-dimensional. there are three inequivalent Fe sites. In the first Fe site, Fe is bonded to six O atoms to form FeO6 octahedra that share corners with three PO4 tetrahedra. There are a spread of Fe–O bond distances ranging from 1.76–1.94 Å. In the second Fe site, Fe is bonded to six O atoms to form FeO6 octahedra that share corners with six PO4 tetrahedra. There are a spread of Fe–O bond distances ranging from 2.00–2.03 Å. In the third Fe site, Fe is bonded to six O atoms to form FeO6 octahedra that share corners with six PO4 tetrahedra. There are a spread of Fe–O bond distances ranging from 2.01–2.04 Å. There are six inequivalent P sites. In the first P site, P is bonded to four O atoms to form PO4 tetrahedra that share corners with three FeO6 octahedra. The corner-sharing octahedra tilt angles range from 28–40°. There are a spread of P–O bond distances ranging from 1.53–1.55 Å. In the second P site, P is bonded to four O atoms to form PO4 tetrahedra that share corners with three FeO6 octahedra. The corner-sharing octahedra tilt angles range from 28–39°. There are a spread of P–O bond distances ranging from 1.53–1.57 Å. In the third P site, P is bonded to four O atoms to form PO4 tetrahedra that share corners with three FeO6 octahedra. The corner-sharing octahedra tilt angles range from 28–40°. There are a spread of P–O bond distances ranging from 1.53–1.56 Å. In the fourth P site, P is bonded to four O atoms to form PO4 tetrahedra that share corners with two FeO6 octahedra. The corner-sharing octahedra tilt angles range from 38–45°. There are a spread of P–O bond distances ranging from 1.53–1.56 Å. In the fifth P site, P is bonded to four O atoms to form PO4 tetrahedra that share corners with two FeO6 octahedra. The corner-sharing octahedra tilt angles range from 38–45°. There is two shorter (1.53 Å) and two longer (1.55 Å) P–O bond length. In the sixth P site, P is bonded to four O atoms to form PO4 tetrahedra that share corners with two FeO6 octahedra. The corner-sharing octahedra tilt angles range from 39–45°. There are a spread of P–O bond distances ranging from 1.53–1.56 Å. There are twenty-seven inequivalent O sites. In the first O site, O is bonded in a bent 150 degrees geometry to one Fe and one P atom. In the second O site, O is bonded in a bent 150 degrees geometry to one Fe and one P atom. In the third O site, O is bonded in a bent 150 degrees geometry to one Fe and one P atom. In the fourth O site, O is bonded in a bent 150 degrees geometry to one Fe and one P atom. In the fifth O site, O is bonded in a bent 150 degrees geometry to one Fe and one P atom. In the sixth O site, O is bonded in a bent 150 degrees geometry to one Fe 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 single-bond geometry to one P atom. In the ninth O site, O is bonded in a single-bond geometry to one P atom. In the tenth O site, O is bonded in a bent 150 degrees geometry to one Fe and one P atom. In the eleventh O site, O is bonded in a bent 150 degrees geometry to one Fe and one P atom. In the twelfth O site, O is bonded in a bent 150 degrees geometry to one Fe and one P atom. In the thirteenth O site, O is bonded in a bent 150 degrees geometry to one Fe and one P atom. In the fourteenth O site, O is bonded in a bent 150 degrees geometry to one Fe and one P atom. In the fifteenth O site, O is bonded in a bent 150 degrees geometry to one Fe and one P atom. In the sixteenth O site, O is bonded in a single-bond geometry to one P atom. In the seventeenth O site, O is bonded in a single-bond geometry to one P atom. In the eighteenth O site, O is bonded in a single-bond geometry to one P atom. In the nineteenth O site, O is bonded in a distorted bent 150 degrees geometry to one Fe and one P atom. In the twentieth O site, O is bonded in a distorted bent 150 degrees geometry to one Fe and one P atom. In the twenty-first O site, O is bonded in a distorted bent 150 degrees geometry to one Fe and one P atom. In the twenty-second O site, O is bonded in a single-bond geometry to one P atom. In the twenty-third O site, O is bonded in a single-bond geometry to one P atom. In the twenty-fourth O site, O is bonded in a single-bond geometry to one P atom. In the twenty-fifth O site, O is bonded in a single-bond geometry to one Fe atom. In the twenty-sixth O site, O is bonded in a single-bond geometry to one Fe atom. In the twenty-seventh O site, O is bonded in a single-bond geometry to one Fe atom.