Etude préliminaire par diffraction X de l'oxyde supraconducteur «quadratique», LaBa2Cu3O7−δ

YBa 2 Cu 3 O 7−x (x≤1) uperconductors from different origins have been studied by electron microscopy and X ray emission. This material has an easy clevage plane parallel to (001) making its observation easy. It has been shown that the preparation reaction was not complete for some superconducting materials. YBa 2 Cu 3 O 7−x crystals can be twinned (mechanical twins, ferroelastic material) but they are generally not, or have few twins. Another oxide has been encountered in epitaxial growth on YBa 2 Cu 3 O 7−x . A superlattice perpendicular to the common c axis has been observed probably due to a regular stacking of the both oxides Cet oxyde quadratique presente une structure perovskite deficitaire ordonnee. Il apparait que la distribution des lacunes oxygene differe de celle observee dans le supraconducteur orthorhombique, YBa 2 Cu 3 O 7− δ. Un modele structural est propose et discute