DOE OSTI2020
NpFe3 is beta Cu3Ti-like structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Np is bonded to twelve Fe atoms to form NpFe12 cuboctahedra that share corners with four equivalent NpFe12 cuboctahedra, corners with eight equivalent FeNp4Fe8 cuboctahedra, edges with eight equivalent NpFe12 cuboctahedra, edges with sixteen equivalent FeNp4Fe8 cuboctahedra, faces with four equivalent NpFe12 cuboctahedra, and faces with fourteen FeNp4Fe8 cuboctahedra. There are eight shorter (2.62 Å) and four longer (2.63 Å) Np–Fe bond lengths. There are two inequivalent Fe sites. In the first Fe site, Fe is bonded to four equivalent Np and eight Fe atoms to form distorted FeNp4Fe8 cuboctahedra that share corners with twelve equivalent FeNp4Fe8 cuboctahedra, edges with eight equivalent NpFe12 cuboctahedra, edges with sixteen FeNp4Fe8 cuboctahedra, faces with four equivalent NpFe12 cuboctahedra, and faces with fourteen FeNp4Fe8 cuboctahedra. There are four shorter (2.62 Å) and four longer (2.63 Å) Fe–Fe bond lengths. In the second Fe site, Fe is bonded to four equivalent Np and eight equivalent Fe atoms to form distorted FeNp4Fe8 cuboctahedra that share corners with four equivalent FeNp4Fe8 cuboctahedra, corners with eight equivalent NpFe12 cuboctahedra, edges with twenty-four FeNp4Fe8 cuboctahedra, faces with six equivalent NpFe12 cuboctahedra, and faces with twelve FeNp4Fe8 cuboctahedra.