Intercroissances des structures de type perovskite et SrO deficitaires en oxygene : Les oxydes Ln2?xSr1+xCu2O6?x/2 (Ln = Sm,Eu, Gd)

New oxides Ln_2?xSr_1+xO_6?x/2 (Ln = Sm, EU, GD), corresponding to oxygen deficient intergrowths of double perovskite and SrO layers have been isolated for 0.70 ≤ x ≤ 0.90. They are characterized by an orthorhombic cell, $\text{a}\text{?}\text{a}{}_{\mathrm{p}}\text{? 3.9}\text{A}\text{?}$, $\text{b}\text{?}\text{3a}{}_{\mathrm{p}}$, and $\text{c}\text{? 20}\text{A}\text{?}$. A structural model has been obtained, showing that this structure, although closely related to that of La_2?xSr_1+xCu₂O_6?x/2+δ exhibits a different distribution of the oxygen vacancies, involving for copper several coordinations. The semi-conductive properties of these compounds, very different from the semi-metallic behaviour of La_2?xSr_1+xCu₂O_6?x/2+δ is explained by the distribution of the oxygen vacancies in the structure.