DOE OSTI2020
Er2Ni12As7 crystallizes in the hexagonal P-6 space group. The structure is three-dimensional. there are two inequivalent Er3+ sites. In the first Er3+ site, Er3+ is bonded to six equivalent As3- atoms to form distorted ErAs6 pentagonal pyramids that share corners with six equivalent NiAs5 square pyramids, corners with twelve NiAs4 tetrahedra, edges with three equivalent NiAs5 square pyramids, edges with nine NiAs4 tetrahedra, and faces with two equivalent ErAs6 pentagonal pyramids. All Er–As bond lengths are 2.95 Å. In the second Er3+ site, Er3+ is bonded to six equivalent As3- atoms to form distorted ErAs6 pentagonal pyramids that share corners with six equivalent NiAs5 square pyramids, corners with twelve NiAs4 tetrahedra, edges with twelve NiAs4 tetrahedra, and faces with two equivalent ErAs6 pentagonal pyramids. All Er–As bond lengths are 2.96 Å. There are four inequivalent Ni+1.25+ sites. In the first Ni+1.25+ site, Ni+1.25+ is bonded to four As3- atoms to form NiAs4 tetrahedra that share corners with two equivalent ErAs6 pentagonal pyramids, corners with two equivalent NiAs5 square pyramids, corners with twelve NiAs4 tetrahedra, edges with three ErAs6 pentagonal pyramids, edges with two equivalent NiAs5 square pyramids, and edges with three NiAs4 tetrahedra. There are a spread of Ni–As bond distances ranging from 2.32–2.40 Å. In the second Ni+1.25+ site, Ni+1.25+ is bonded to four As3- atoms to form NiAs4 tetrahedra that share corners with four ErAs6 pentagonal pyramids, corners with two equivalent NiAs5 square pyramids, corners with ten NiAs4 tetrahedra, an edgeedge with one ErAs6 pentagonal pyramid, edges with four equivalent NiAs5 square pyramids, and edges with three NiAs4 tetrahedra. There are a spread of Ni–As bond distances ranging from 2.27–2.38 Å. In the third Ni+1.25+ site, Ni+1.25+ is bonded to four As3- atoms to form NiAs4 tetrahedra that share corners with two equivalent ErAs6 pentagonal pyramids, corners with four equivalent NiAs5 square pyramids, corners with ten NiAs4 tetrahedra, edges with three ErAs6 pentagonal pyramids, an edgeedge with one NiAs5 square pyramid, and edges with four NiAs4 tetrahedra. There are a spread of Ni–As bond distances ranging from 2.35–2.42 Å. In the fourth Ni+1.25+ site, Ni+1.25+ is bonded to five As3- atoms to form distorted NiAs5 square pyramids that share corners with four ErAs6 pentagonal pyramids, corners with four equivalent NiAs5 square pyramids, corners with eight NiAs4 tetrahedra, an edgeedge with one ErAs6 pentagonal pyramid, edges with four equivalent NiAs5 square pyramids, and edges with seven NiAs4 tetrahedra. There are a spread of Ni–As bond distances ranging from 2.43–2.62 Å. There are three inequivalent As3- sites. In the first As3- site, As3- is bonded in a 9-coordinate geometry to nine Ni+1.25+ atoms. In the second As3- site, As3- is bonded in a 9-coordinate geometry to two equivalent Er3+ and seven Ni+1.25+ atoms. In the third As3- site, As3- is bonded in a 9-coordinate geometry to two equivalent Er3+ and seven Ni+1.25+ atoms.