De nouveaux isotypes lacunaires de CeNiSi2: Les germaniures RCoxGe2, R = Y, La-Sm, Gd-Lu, 0 < x ≦ 1

Abstract The new germanides RCo x Ge 2 , R = Y, La-Sm, Gd-Lu, crystallize in the orthorhombic CeNiSi 2 -type structure with cobalt vacancies. Their cobalt deficiency regularly increases through the series according to the lanthanide contraction: x vary from 1 to 0.34 between R = La and Lu. The structure of NdCo 0.83 Ge 2 was refined from single-crystal data to a conventional R value of 0.034 for 210 independent reflections (R w = 0.033). The La, Y and Lu compounds show Pauli paramagnetism and are not superconducting above 1.5 K.