DOE OSTI2020
Ho2Ni12As7 crystallizes in the hexagonal P-6 space group. The structure is three-dimensional. there are two inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded to six equivalent As3- atoms to form distorted HoAs6 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 HoAs6 pentagonal pyramids. All Ho–As bond lengths are 2.98 Å. In the second Ho3+ site, Ho3+ is bonded to six equivalent As3- atoms to form distorted HoAs6 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 HoAs6 pentagonal pyramids. All Ho–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 HoAs6 pentagonal pyramids, corners with two equivalent NiAs5 square pyramids, corners with twelve NiAs4 tetrahedra, edges with three HoAs6 pentagonal pyramids, edges with two equivalent NiAs5 square pyramids, and edges with three NiAs4 tetrahedra. There are two shorter (2.35 Å) and two longer (2.40 Å) Ni–As bond lengths. 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 HoAs6 pentagonal pyramids, corners with two equivalent NiAs5 square pyramids, corners with ten NiAs4 tetrahedra, an edgeedge with one HoAs6 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 2.25–2.40 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 HoAs6 pentagonal pyramids, corners with four equivalent NiAs5 square pyramids, corners with ten NiAs4 tetrahedra, edges with three HoAs6 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 2.37–2.42 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 HoAs6 pentagonal pyramids, corners with four equivalent NiAs5 square pyramids, corners with eight NiAs4 tetrahedra, an edgeedge with one HoAs6 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 2.44–2.64 Å. There are three inequivalent As3- sites. In the first As3- site, As3- is bonded in a 9-coordinate geometry to two equivalent Ho3+ and seven Ni+1.25+ atoms. In the second As3- site, As3- is bonded in a 9-coordinate geometry to two equivalent Ho3+ and seven Ni+1.25+ atoms. In the third As3- site, As3- is bonded in a 9-coordinate geometry to nine Ni+1.25+ atoms.