Les oxydes A2BaCuO5 (A = Y,Sm, Eu,Gd, Dy,Ho, Er,Yb)

A series of new phases, A₂BaCuO₅ (A = Y, Sm, Eu, Gd, Dy, Ho, Er, Yb), has been isolated. These compounds are orthorhombic, with $\text{a ? 7.1, b ? 12.2}$, and $\text{c ? 5.6}$Å. The probable space groups deduced from the electron diffraction patterns are Pbnm and Pbn2₁. The structure has been resolved from X-ray powder patterns. The framework can be considered as built up from distorted monocapped trigonal prisms AO₇ which share one triangular face forming A₂O₁₁ blocks. The edge-sharing A₂O₁₁ blocks form a three-dimensional network which delimits cavities where Ba²⁺ and Cu²⁺ are located. Barium is coordinated to 11 oxygen atoms, while the coordination polyhedron of copper is a distorted tetragonal pyramid CuO₅.