The crystal structures of the ternary intermetallics RE 2Pd2Cd (RE = Nd, Sm, Gd, Dy) and RE 2Ga2Mg (RE = Tb, Er, Tm, Lu) at 90 K

Abstract The crystal structures of the U 3 Si 2 -related intermetallic compounds RE 2 Pd 2 Cd ( RE = Nd, Sm, Gd, Dy) and RE 2 Ga 2 Mg ( RE = Tb, Er, Tm, Lu) were studied from single crystal X-ray diffraction data at T = 90 K in order to understand the slightly enhanced U 33 displacements of the 2 a positions in their room temperature structures. The compounds Sm 2 Pd 2 Cd, Gd 2 Pd 2 Cd and Dy 2 Pd 2 Cd show a decrease of the ratio of U 33 to U 11 for the cadmium atoms, leading to a more isotropic behavior at low temperature, keeping the P 4/ mbm space group symmetry. Nd 2 Pd 2 Cd shows a translationengleiche symmetry reduction to space group P 4 bm along with a weak puckering effect with shorter (342.7 pm) and longer (345.7 pm) Cd–Nd distances within the Cd@Nd 8 square prisms. This new, non-centrosymmetric superstructure variant was also observed for the magnesium compounds Tb 2 Ga 2.069 Mg 0.931 , Er 2 Ga 2.104 Mg 0.896 , Tm 2 Ga 2.097 Mg 0.903 and Lu 2 Ga 2.173 Mg 0.827 , which show small degrees of Mg/Ga mixing.