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

Abstract  

The series of rare earth metal (RE)-rich intermetallics RE ₄ TAl and RE ₄ TIn (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]3mF\bar{4}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 RE ₆ T trigonal prisms which form a rigid network with adamantane-like topology. Large cavities within these networks are filled with empty RE ₆ octahedra and Al₄, In₄, Mg₄, or Cd₄ tetrahedra, respectively. Some of the RE ₄ TAl and RE ₄ TIn 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.