DOE OSTI2020
FeTa is Frank-Kasper $\mu$ Phase-like structured and crystallizes in the trigonal R-3m space group. The structure is three-dimensional. there are seven inequivalent Ta sites. In the first Ta site, Ta is bonded in a 6-coordinate geometry to eight Ta and six equivalent Fe atoms. There are a spread of Ta–Ta bond distances ranging from 2.66–3.12 Å. All Ta–Fe bond lengths are 2.66 Å. In the second Ta site, Ta is bonded in a 8-coordinate geometry to eight Ta and six equivalent Fe atoms. There are a spread of Ta–Ta bond distances ranging from 2.76–3.11 Å. All Ta–Fe bond lengths are 2.68 Å. In the third Ta site, Ta is bonded in a 9-coordinate geometry to seven Ta and nine equivalent Fe atoms. There are three shorter (2.84 Å) and three longer (2.91 Å) Ta–Ta bond lengths. There are three shorter (2.83 Å) and six longer (2.99 Å) Ta–Fe bond lengths. In the fourth Ta site, Ta is bonded in a 12-coordinate geometry to four Ta and twelve Fe atoms. All Ta–Ta bond lengths are 2.91 Å. There are a spread of Ta–Fe bond distances ranging from 2.77–2.93 Å. In the fifth Ta site, Ta is bonded in a 6-coordinate geometry to nine Ta and six Fe atoms. All Ta–Ta bond lengths are 2.81 Å. There are three shorter (2.79 Å) and three longer (2.83 Å) Ta–Fe bond lengths. In the sixth Ta site, Ta is bonded in a 6-coordinate geometry to nine Ta and six Fe atoms. There are three shorter (2.78 Å) and three longer (2.82 Å) Ta–Fe bond lengths. In the seventh Ta site, Ta is bonded to six equivalent Ta and six equivalent Fe atoms to form distorted TaTa6Fe6 cuboctahedra that share corners with twelve equivalent FeTa8Fe4 cuboctahedra, edges with six equivalent TaTa6Fe6 cuboctahedra, and faces with eighteen equivalent FeTa8Fe4 cuboctahedra. All Ta–Fe bond lengths are 2.55 Å. There are three inequivalent Fe sites. In the first Fe site, Fe is bonded to seven Ta and five Fe atoms to form FeTa7Fe5 cuboctahedra that share corners with fifteen FeTa7Fe5 cuboctahedra, edges with five FeTa8Fe4 cuboctahedra, and faces with thirteen FeTa7Fe5 cuboctahedra. There are a spread of Fe–Fe bond distances ranging from 2.42–2.46 Å. In the second Fe site, Fe is bonded to eight Ta and four equivalent Fe atoms to form distorted FeTa8Fe4 cuboctahedra that share corners with two equivalent TaTa6Fe6 cuboctahedra, corners with thirteen FeTa7Fe5 cuboctahedra, edges with five FeTa8Fe4 cuboctahedra, faces with three equivalent TaTa6Fe6 cuboctahedra, and faces with ten equivalent FeTa8Fe4 cuboctahedra. There are two shorter (2.38 Å) and two longer (2.49 Å) Fe–Fe bond lengths. In the third Fe site, Fe is bonded to six equivalent Ta and six equivalent Fe atoms to form FeTa6Fe6 cuboctahedra that share corners with twelve equivalent FeTa7Fe5 cuboctahedra, edges with six equivalent FeTa6Fe6 cuboctahedra, and faces with eighteen equivalent FeTa7Fe5 cuboctahedra.