Crystallogeometry relations and latent phases in the Y-Ba-Cu-O compounds

Abstract This paper deals with a new description of the structure of the high-Tc superconductors. In particular, we show that the structure of the Y–Ba–Cu–0 compounds can be described as the result of an order-disorder phase transition from a highsymmetry latent phase Pm3m. The crystallogeometry relations between the high-symmetry phase Pm3m and the low-symmetry phases P4/mmm and Pmmm give, in particular, the changing of the symmetry of translations and the equivalent positions of the different atoms. This point of view allows us to describe the modification of the structure, associated with changing chemical composition with the critical formula YBa2Cu3O6,44 in agreement with the experimental phase diagram.