De nouvelles séries de germaniures, isotypes de U 4Re 7Si 6, ThCr 2Si 2 et CaBe 2Ge 2, dans les systèmes ternaires RTGe où R est un élément des terres rares et T ≡ Ru, Os, Rh, Ir: supraconductivité de LaIr 2Ge 2

Abstract

Fifty-one new ternary germanides have been characterized by X-ray powder diffraction: 19 with the U 4Re 7Si 6-type structure: Lu 4Ru 7Ge 6, R 4Os 7Ge 6 (R ≡ Er, …, Lu); R 4Rh 7Ge 6 (R ≡ Dy, …, Lu) and R 4Ir 7Ge 6 (R ≡ Y, Tb, …, Lu); 28 with the ThCr 2Si 2-type structure: RRu 2Ge 2 and RRh 2Ge 2 (R ≡ Y, La, …, Yb); EuIr 2Ge 2; 4 with the CaBe 2Ge 2-type structure: RIr 2Ge 2 (R ≡ La, …, Nd). Three others require further study: SmIr 2Ge 2 and TbIr 2Ge 2 are probably isostructural with CaBe 2Ge 2, in spite of their singular parameters and GdIr 2Ge 2, which has an orthorhombic structure, should be a new variant of the CaBe 2Ge 2-type. The observed structural changes are discussed. LaIr 2Ge 2 exhibits a superconducting transition at T C = 1.5 K.