Polymorphism in the Germanides REPdGe with the Heavy Rare Earth Elements

Abstract

The structures of the equiatomic germanides REPdGe with the heavy rare earth elements have been reinvestigated with respect to palladium-germanium ordering. The samples were prepared by arc-melting of the elements followed by annealing procedures in sealed silica ampoules at different temperatures. The structures of YPdGe, HT-TbPdGe, LT-DyPdGe, HT-DyPdGe, LT-HoPdGe, HT-HoPdGe, ErPdGe, and TmPdGe, and of the new germanide LuPdGe, were refined from single crystal diffractometer data. LT-DyPdGe and LT-HoPdGe crystallize with the YPdSi-type structure, space group Pmmn. The other germanides crystallize with the non-centrosymmetric YbAuSn structure, space group Imm2. All structures are orthorhombically-distorted superstructure variants of AlB2, and they show strong intralayer Pd-Ge bonding within the ordered Pd3Ge3 hexagons. There is weak Pd-Ge and Pd-Pd interlayer bonding. The crystal chemical relationship between the different superstructures is discussed.