Superconductive percolation in Bi-based superconductor/Bi-based insulator composites:: case of Bi-2223/Bi-2310 and Bi-2212/BiFeO3

Preparation of Bi-2223/Bi-2310 and Bi-2212/BiFeO3 composites has been performed so as to obtain some active composites where the superconductive properties of Bi-2223 or Bi-2212 can be modified using a property of the insulating phase. In both eases superconductive percolation was obtained, but only in the case of a Bi-2223 (or Bi-2712)/Bi-2310 composite was no (or very weak) chemical reaction observed during sintering. Since the superconductive percolation threshold was obtained in this case for a concentration of Bi-2223 or Bi-2212 lower than 20%, a special composite model had to be considered. The Bi-2212/BiFeO3 system is very interesting due to the ferroic properties of BiFeO3. Superconductive percolation was achieved with this mixture too, but with more difficulties because of a chemical reaction occurring between the two compounds during sintering. A study of the properties of these composites has been performed and will be briefly described in what follows. The good quality of the Bi-2223(or Bi-2212)/B1-2310 composite enables us to expect same future applications.