Abstract:

The deposits on anode and cathode in electrocrystallization of Ba-K-Bi-O superconductor from molten salts were characterized by using XPS and XRD. The morphology of resulting Ba-K-Bi-O crystals was analyzed by using SEM. The results show that the deposit on anode is superconducting Ba-K-Bi-O single crystals which grow as steps on the crystal faces. The deposit on cathode is controlled by the melt composition: the deposit is metallic Bi when the water content of KOH is relatively high; the deposit is Bi2O3 when the water content is relatively low and the melt contains NO3-; the deposit is metallic Zn when ZnO is added into the melt. The mechanism of electrocrystallization of Ba-K-Bi-O superconductor is discussed. We suggest that Bi ions in the melt may form complex ions with OH- ions, the latter migrate to the anode due to the action of convection, diffusion and electric migration. The formation of Ba-K-Bi-O and incorporation of Ba into the crystals may be related to highly oxidized species (e.g. O1-type oxygen)formed at the anode in the strong alkali melt.

Key words: Ba-K-Bi-O superconductor, Electrocrystallization, Molten salts