ORDER-DISORDER MECHANISM AND A PHENOMENOLOGICAL MODEL IN (BI,PB)-SR-CA-CU-O

We established a relationship between the structures of the bismuth hi gh T-c superconducting compounds and a symmetry of disordered perovski te type. This description which we propose, leads to considering the s tructures of these materials in terms of a commensurate superstructure obtained from a latent perovskite structure of space group Im3m. A ph enomenological model was elaborated in order to describe the two types of modulations realized in these compounds.