AnTAlSi (An = Ce, Th, U, Np; T = Ni, Co): Actinide Intermetallics with Disordered GdFeSi Structure Type Grown from Metal Flux.

AnTAlSi (An = Ce, Th, U, Np; T = Ni, Co) were synthesized in metal flux reactions carried out in aluminum/gallium melts. In previous work, UTAlSi (T = Co, Ni) analogues were formed by arc-melting U:T:Si and reacting this mixture in Al/Ga flux. However, in the current work, all compounds were synthesized by using AnO reactants, taking advantage of the ability of the aluminum in the flux to act as both solvent and reducing agent. While reactions with T = Co yielded hexagonal GdFeSi-type quaternary phases for all An, reactions with T = Ni produced these compounds only with An = U and Np. For reactions with An = Ce and Th, the reactions led instead to the formation of AnNiSiAlGa phases, with the tetragonal KCuS structure type. Attempts to synthesize plutonium analogues PuTAlSi were also unsuccessful, producing the previously reported PuCoGa and PuNiSi instead. Magnetic data collected on the neptunium analogues NpTAlSi (T = Ni, Co) show antiferromagnetic coupling at low temperatures and indicate a tetravalent state for the Np ions.