SYNTHESIS AND CHEMISTRY OF THE NEW Y-BASED AND Bi-BASED HIGH TEMPERATURE SUPERCONDUCTING PEROVSKITES

Chemical synthesis of the new high Tc oxides using solid state reactions or solution techniques is shown. A solution process which allows the preparation of both homogeneous and dense ceramics and of superconducting thick films has been developed for the YBa2Cu3O7 system. Physical measurements performed on homogeneous YBa2Cu3-xCoxOy samples have shown that the Co substitution, associated with an uptake of oxygen, takes place on the Cu-O chains and that Tc is depressed, leading ultimately to antiferromagnetic insulators whose magnetic structures are shown. Three phase of general formula Bi2Sr2Can-1CunOy with n = 1,2 and 3 have been isolated in the Bi system and characterized for their structural and physical properties. These phases crystallize in the same pseudotetragonal unit cell differing one from the next by the stacking sequence along the c-axis, with the main feature being the presence of a sheared Bi-O double layer. The T'cs of the n = 1,2 and 3 phases are 10 K, 85 K and 110 K respectively, but because of phase intergrowth, these values depend upon sample processing, making chemical substitutions within the Bi system quite complex as is discussed. Finally, we succeeded in making superconducting thick films (having zero resistance around 100 K) of the Bi-based and T1-based materials via the decomposition of aqueous-glycerol solutions containing the salts of the elements