New rare earth-rich aluminides and indides with cubic Gd4RhIn-type structure

The series of rare earth metal (RE)-rich intermetallics RE4TAl and RE4TIn (T = Ru, Rh, Ir) were synthesized by induction melting of the elements in sealed tantalum tubes. These compounds crystallize with the cubic Gd4RhIn-type structure, space group F (4) over bar 3m. The structures of eight crystals (including the isotypic compounds Ce4RuMg and Ce4RuCd) have been refined from X-ray single-crystal diffractometer data. The structures are composed of condensed RE6T trigonal prisms which form a rigid network with adamantane-like topology. Large cavities within these networks are filled with empty RE6 octahedra and Al-4, In (4), Mg (4), or Cd-4 tetrahedra, respectively. Some of the RE4TAl and RE4TIn show small homogeneity ranges that result from small degrees of Al/T and In/T mixing on the 16e sites. All cerium compounds show small anomalies in the plots of the cell volumes. This is confirmed by temperature-dependent magnetic susceptibility measurements. Ce4RuMg, Ce4RuCd, Ce4RuAl, and Ce4RuIn show intermediate cerium valence and no magnetic ordering down to 3 K. Ce4RhAl shows essentially trivalent cerium.