NOVEL TECHNIQUES FOR CHARACTERIZATION AND KINETICS STUDIES OF Bi-2223 CONDUCTORS

Abstract

The Bi-2223 high temperature superconductor (HTS) powder-in-tube (PIT) tape and long-lengths of conductors with unique performance has provided the ability to construct a wide range of HTS electric power components. Oxygen doping, cation doping, phase transition and strain all strongly influence the superconducting transition temperature Tc. We report to characterize these materials by thermal analysis, X-ray diffraction and scanning electron microscopy. Activation energies and frequency factors employing different models were evaluated. It was observed that both peritectic transition and reaction rates were dependent on ambient atmosphere. X-ray diffraction results showed that volume fraction of the high-Tc (2223) phase decreases and that of low-Tc (2212) phase increases with the increase of rare-earth ion content. SEM studies revealed that the conversion of 2212 pre-cursor phase to 2223 was significantly influenced by the sintering atmosphere and the lower partial pressure of O2 which promoted faster conversion of 2212 phase and smaller 2223 grain size. The critical current densities of silver sheathed tapes using the powder-in-tube were found to be in the range 7 x 108 A m-2. A possible explanation for the difference in phase transformation and the effects on the critical current was discussed.