Superconducting and magnetic properties of ternary silicides in some rare earth-noble metal (Rh or Ir)-silicon systems

New families of ternary silicides have been prepared in the RE - Rh or Ir -Si systems and the crystal structures have been determined: RERh₃Si₂, RE₂Rh₃Si₅, RE₂RhSi₃ (RE = Y, La → Er), RERhSi (Y, La, Gd → Er), REIrSi (RE = La, Ce, Nd), RERhSi₂ and REIrSi₂ (RE = La → Gd). The RE₂RhSi₃ compounds crystallize with a new structural type, the other ones are isostructural with already known silicides or borides. Some of the silicides studied whose rare earths are diamagnetic (Y, La) show superconducting transitions above 1.6 K. They have been compared with other superconducting ternary borides, silicides, germanides and phosphides containing rare earths and noble metals. Except the phases with Y and La which are diamagnetic or show Pauli paramagnetism, the other materials order magnetically at low temperature. The onset of magnetic transitions vs. field has been observed for some compounds below 20 kOe at 4.2 K.