DOE OSTI2020
Hf3Mn4Si6 crystallizes in the tetragonal P4_2/mbc space group. The structure is three-dimensional. there are three inequivalent Hf4+ sites. In the first Hf4+ site, Hf4+ is bonded to seven Si4- atoms to form HfSi7 pentagonal bipyramids that share corners with two equivalent MnSi6 octahedra, corners with eight HfSi7 pentagonal bipyramids, edges with three HfSi7 pentagonal bipyramids, faces with two equivalent MnSi6 octahedra, and faces with three HfSi7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 51°. There are a spread of Hf–Si bond distances ranging from 2.60–2.84 Å. In the second Hf4+ site, Hf4+ is bonded to seven Si4- atoms to form HfSi7 pentagonal bipyramids that share corners with two equivalent MnSi6 octahedra, corners with six HfSi7 pentagonal bipyramids, edges with two equivalent HfSi7 pentagonal bipyramids, faces with two equivalent MnSi6 octahedra, and faces with six HfSi7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 51°. There are a spread of Hf–Si bond distances ranging from 2.72–2.84 Å. In the third Hf4+ site, Hf4+ is bonded to seven Si4- atoms to form HfSi7 pentagonal bipyramids that share corners with four equivalent MnSi6 octahedra, corners with six HfSi7 pentagonal bipyramids, an edgeedge with one HfSi7 pentagonal bipyramid, and faces with five HfSi7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 38–40°. There are a spread of Hf–Si bond distances ranging from 2.68–2.82 Å. There are three inequivalent Mn3+ sites. In the first Mn3+ site, Mn3+ is bonded in a 6-coordinate geometry to six Si4- atoms. There are a spread of Mn–Si bond distances ranging from 2.40–2.46 Å. In the second Mn3+ site, Mn3+ is bonded in a 7-coordinate geometry to seven Si4- atoms. There are a spread of Mn–Si bond distances ranging from 2.35–2.85 Å. In the third Mn3+ site, Mn3+ is bonded to six Si4- atoms to form distorted MnSi6 octahedra that share corners with eight HfSi7 pentagonal bipyramids, faces with two equivalent MnSi6 octahedra, and faces with four HfSi7 pentagonal bipyramids. There are a spread of Mn–Si bond distances ranging from 2.39–2.48 Å. There are six inequivalent Si4- sites. In the first Si4- site, Si4- is bonded in a 6-coordinate geometry to one Hf4+, four equivalent Mn3+, and one Si4- atom. The Si–Si bond length is 2.35 Å. In the second Si4- site, Si4- is bonded in a 9-coordinate geometry to five Hf4+ and four Mn3+ atoms. In the third Si4- site, Si4- is bonded in a 12-coordinate geometry to four Hf4+ and four equivalent Mn3+ atoms. In the fourth Si4- site, Si4- is bonded in a 9-coordinate geometry to four Hf4+ and five Mn3+ atoms. In the fifth Si4- site, Si4- is bonded in a 5-coordinate geometry to one Hf4+ and six Mn3+ atoms. In the sixth Si4- site, Si4- is bonded in a 10-coordinate geometry to six Hf4+, two equivalent Mn3+, and two equivalent Si4- atoms. Both Si–Si bond lengths are 2.52 Å.