Effect of rare-earth(Eu, Yb and Ag) substitutions on superconducting properties of the Bi1.7Pb0.3Sr2Ca2-xRx(R=Eu, Yb, and Ag)Cu3Oy system

摘要

The superconducting properties of Bi1.7Pb0.3Sr2Ca2-xRx(R=Eu, Yb, and Ag)Cu3Oy have been investigated by X-raydiffraction, electrical resistance and the peritectic transition ofthese superconductors was studied kinetically under differentatmospheres and temperature gradients. X-ray diffraction resultsshow that the volume fraction of the high-Tc (2223) phasedecreases and that of the low-Tc (2212) phase increases as Eu, Yband Ag concentrations increase. The resistivity measurementsreveal that the Tc onset decreases down to 100K for Eu, 85K forYb and 106k for Ag concentrations. These results are explained onthe basis of possible variations of hole concentration with trivalentrate earth ion substitutions. Activation energies and frequencyfactors for crystallisation were determined by non-isothermaldifferential thermal analysis (DTA), employing different models. Itwas foud that both peritectic transition and reaction rate weredependent on the ambient atmosphere.Kinetic studies underdifferent atmospheres revealed that the thermal stability of Bi-2212 phase was greatly enhanced under oxygen atmosphere.