Crystal structure and physical properties of new ternary silicides R 4T 13X 9 (R, rare earth or uranium; T, rhodium or iridium; X, silicon or germanium)

Abstract

New ternary silicides have been discovered with the general formula R 4T 13X 9, where R is a rare earth or uranium, T is rhodium or iridium and X is silicon or germanium. The crystal structure has been solved on a single crystal. The symmetry is orthorhombic with space group Pnmm. The lattice constants for Er 4Ir 13Si 9 are a = 18.848(3) A ̊ , b = 10.918(2) A ̊ and c = 3.9153(5) A ̊ . The formation of the various members of this new family is in competition with that of the well-known ternary silicides RT 3X 2. Their existence as a function of the various elements (rare earth and transition metals) is discussed. The magnetic properties of the iridium-based compounds are presented. All the samples containing a paramagnetic rare earth are magnetically ordered at low temperature. U 4Ir 13Si 9 and U 4Ir 13Ge 9 exhibit two ordering transition temperatures: 18 and 6.4. K for the silicide and 25 and 7 K for the germanide.