Effect of doping on properties of Bi-based superconductors

The influence of alkaline metals on the properties of Bi-based high temperature superconductors has been studied. The samples Bi3.2Pb0.8Sr4Ca5Cu7AxOy (A=Li or Cs, x=0,0.2,0.4,0.6,0.8) were prepared and characterized by XRD analysis, resistivity and susceptibility measurements. The results showed that all the doped samples had Tc in the range 104-110.5 K. The transition width ΔT of the Bi-2223 phase in the lithium doped samples increased with higher concentration of dopant. In the cesium doped samples the transition width decreased with increasing Cs level up to x=0.6 then slightly increased. Values of Jc of lithium containing samples decreased with increasing amount of doped lithium. Samples doped with lower amount of cesium (x=0.2,0.4) had notably higher critical current densities than the undoped standard. Nevertheless, Jc's of samples with higher amount of cesium were worse than that of the standard. Lithium had a positive influence on the formation of Bi-2223 phase in all concentration except x=0.6. In samples doped with cesium the volume of Bi-2223 phase was higher than in the undoped sample as well, the values were not as high as in lithium doped samples. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)