Abstract
One known and nine new quaternary aluminides in the Al-rich region of R–T–Ag–Al (R = Y, Ce, Pr, Nd, Sm, and Gd, T = V, Nb, Ta, Cr, and Mo) systems were synthesized by arc melting and their crystal structures were studied by X-ray powder diffraction. The crystal structures of the compounds R3T(Ag,Al)20Al12 (R = Ce, Pr, Nd, and Sm, T = V, Nb, Ta, Cr, and Mo) and R3TAgx(Ag,Al)20Al12 (R = Y and Gd, T = Ta) belong to new structure types: Ce3Ta (Ag,Al)20Al12 (Pearson symbol сP36, space group Pm-3m, a = 8.6675(2) Å) and Gd3TaAgx(Ag,Al)20Al12 (сP4912.86, Pm-3m, a = 8.6158(5) Å), respectively. Within the rows of isotypic compounds the unit-cell parameter increases with increasing metallic radius of the rare-earth or d-element atom. The structure type Ce3Ta (Ag,Al)20Al12 (Ce3TaAg7.97Al24.03) is a partly ordered quaternary substitution derivative of the structure type BaHg11, whereas Gd3TaAgx(Ag,Al)20Al12 (Gd3TaAg8.89Al23.25) is a distorted fill-in quaternary substitution variant of the same prototype. The latter can also be described as a derivative of the structure type Y3TaNi6+xAl26.
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