DOE OSTI2020
Ac3Nb is Uranium Silicide-like structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. there are two inequivalent Ac sites. In the first Ac site, Ac is bonded to eight Ac and four equivalent Nb atoms to form distorted AcAc8Nb4 cuboctahedra that share corners with twelve equivalent AcAc8Nb4 cuboctahedra, edges with eight equivalent NbAc12 cuboctahedra, edges with sixteen AcAc8Nb4 cuboctahedra, faces with four equivalent NbAc12 cuboctahedra, and faces with fourteen AcAc8Nb4 cuboctahedra. There are four shorter (3.66 Å) and four longer (3.71 Å) Ac–Ac bond lengths. All Ac–Nb bond lengths are 3.71 Å. In the second Ac site, Ac is bonded to eight equivalent Ac and four equivalent Nb atoms to form distorted AcAc8Nb4 cuboctahedra that share corners with four equivalent AcAc8Nb4 cuboctahedra, corners with eight equivalent NbAc12 cuboctahedra, edges with twenty-four AcAc8Nb4 cuboctahedra, faces with six equivalent NbAc12 cuboctahedra, and faces with twelve AcAc8Nb4 cuboctahedra. All Ac–Nb bond lengths are 3.66 Å. Nb is bonded to twelve Ac atoms to form NbAc12 cuboctahedra that share corners with four equivalent NbAc12 cuboctahedra, corners with eight equivalent AcAc8Nb4 cuboctahedra, edges with eight equivalent NbAc12 cuboctahedra, edges with sixteen equivalent AcAc8Nb4 cuboctahedra, faces with four equivalent NbAc12 cuboctahedra, and faces with fourteen AcAc8Nb4 cuboctahedra.