DOE OSTI2020
Er2Bi2O7 crystallizes in the monoclinic P2_1 space group. The structure is three-dimensional. there are four inequivalent Er3+ sites. In the first Er3+ site, Er3+ is bonded to seven O2- atoms to form distorted ErO7 pentagonal bipyramids that share corners with three BiO5 trigonal bipyramids, edges with five ErO7 pentagonal bipyramids, and edges with three BiO5 trigonal bipyramids. There are a spread of Er–O bond distances ranging from 2.20–2.45 Å. In the second Er3+ site, Er3+ is bonded to seven O2- atoms to form distorted ErO7 pentagonal bipyramids that share corners with three BiO5 trigonal bipyramids, edges with five ErO7 pentagonal bipyramids, and edges with three BiO5 trigonal bipyramids. There are a spread of Er–O bond distances ranging from 2.21–2.44 Å. In the third Er3+ site, Er3+ is bonded to seven O2- atoms to form distorted ErO7 pentagonal bipyramids that share corners with three BiO5 trigonal bipyramids, edges with five ErO7 pentagonal bipyramids, and edges with three BiO5 trigonal bipyramids. There are a spread of Er–O bond distances ranging from 2.21–2.44 Å. In the fourth Er3+ site, Er3+ is bonded to seven O2- atoms to form distorted ErO7 pentagonal bipyramids that share corners with three BiO5 trigonal bipyramids, edges with five ErO7 pentagonal bipyramids, and edges with three BiO5 trigonal bipyramids. There are a spread of Er–O bond distances ranging from 2.19–2.45 Å. There are four inequivalent Bi4+ sites. In the first Bi4+ site, Bi4+ is bonded to five O2- atoms to form distorted BiO5 trigonal bipyramids that share corners with three ErO7 pentagonal bipyramids, a cornercorner with one BiO5 trigonal bipyramid, edges with three ErO7 pentagonal bipyramids, and an edgeedge with one BiO5 trigonal bipyramid. There are a spread of Bi–O bond distances ranging from 2.18–2.45 Å. In the second Bi4+ site, Bi4+ is bonded to five O2- atoms to form distorted BiO5 trigonal bipyramids that share corners with three ErO7 pentagonal bipyramids, a cornercorner with one BiO5 trigonal bipyramid, edges with three ErO7 pentagonal bipyramids, and an edgeedge with one BiO5 trigonal bipyramid. There are a spread of Bi–O bond distances ranging from 2.08–2.26 Å. In the third Bi4+ site, Bi4+ is bonded to five O2- atoms to form distorted BiO5 trigonal bipyramids that share corners with three ErO7 pentagonal bipyramids, a cornercorner with one BiO5 trigonal bipyramid, edges with three ErO7 pentagonal bipyramids, and an edgeedge with one BiO5 trigonal bipyramid. There are a spread of Bi–O bond distances ranging from 2.15–2.38 Å. In the fourth Bi4+ site, Bi4+ is bonded to five O2- atoms to form distorted BiO5 trigonal bipyramids that share corners with three ErO7 pentagonal bipyramids, a cornercorner with one BiO5 trigonal bipyramid, edges with three ErO7 pentagonal bipyramids, and an edgeedge with one BiO5 trigonal bipyramid. There are a spread of Bi–O bond distances ranging from 2.11–2.32 Å. There are fourteen inequivalent O2- sites. In the first O2- site, O2- is bonded to two Er3+ and two Bi4+ atoms to form a mixture of distorted edge and corner-sharing OEr2Bi2 trigonal pyramids. In the second O2- site, O2- is bonded to three Er3+ and one Bi4+ atom to form a mixture of distorted edge and corner-sharing OEr3Bi tetrahedra. In the third O2- site, O2- is bonded to two Er3+ and two Bi4+ atoms to form distorted OEr2Bi2 tetrahedra that share corners with four OEr3Bi tetrahedra, edges with three OEr3Bi tetrahedra, and an edgeedge with one OEr2Bi2 trigonal pyramid. In the fourth O2- site, O2- is bonded in a trigonal planar geometry to two Er3+ and one Bi4+ atom. In the fifth O2- site, O2- is bonded to three Er3+ and one Bi4+ atom to form distorted OEr3Bi tetrahedra that share corners with six OEr3Bi tetrahedra, edges with three OEr2Bi2 tetrahedra, and an edgeedge with one OEr2Bi2 trigonal pyramid. In the sixth O2- site, O2- is bonded in a trigonal planar geometry to two Er3+ and one Bi4+ atom. In the seventh O2- site, O2- is bonded in a bent 150 degrees geometry to two Bi4+ atoms. In the eighth O2- site, O2- is bonded in a bent 150 degrees geometry to two Bi4+ atoms. In the ninth O2- site, O2- is bonded in a trigonal planar geometry to two Er3+ and one Bi4+ atom. In the tenth O2- site, O2- is bonded to three Er3+ and one Bi4+ atom to form distorted OEr3Bi tetrahedra that share corners with five OEr3Bi tetrahedra, a cornercorner with one OEr2Bi2 trigonal pyramid, edges with three OEr3Bi tetrahedra, and an edgeedge with one OEr2Bi2 trigonal pyramid. In the eleventh O2- site, O2- is bonded in a trigonal planar geometry to two Er3+ and one Bi4+ atom. In the twelfth O2- site, O2- is bonded to two Er3+ and two Bi4+ atoms to form distorted OEr2Bi2 tetrahedra that share corners with four OEr2Bi2 tetrahedra and edges with four OEr3Bi tetrahedra. In the thirteenth O2- site, O2- is bonded to three Er3+ and one Bi4+ atom to form distorted OEr3Bi tetrahedra that share corners with five OEr3Bi tetrahedra, a cornercorner with one OEr2Bi2 trigonal pyramid, and edges with four OEr2Bi2 tetrahedra. In the fourteenth O2- site, O2- is bonded to two Er3+ and two Bi4+ atoms to form distorted OEr2Bi2 tetrahedra that share corners with two OEr3Bi tetrahedra, corners with two equivalent OEr2Bi2 trigonal pyramids, and edges with four OEr3Bi tetrahedra.