Gd-substituted Bi-2223 superconductor

摘要

The effects of gadolinium doping at calcium site on theudnormal and superconducting properties of Bi-2223 system were studied.The Gd-doped (BiPb)-2223 series of specimens, namely Batch I, II and III were sintered at three different sintering temperatures 830, 850 and 895$^{circ}$C respectively. The properties investigated are (1)the normal state resistivity with a view to study metal-to-insulatorudtransition, (2) the XRD patterns of the specimens with a view to study the relative composition of (BiPb)-2212 and (BiPb)-2223 phases and (3) the superconducting fluctuation behaviour (SFB) with a view to determine the effect of doping, if any, on the dimensionality of the fluctuation conductivity of the system. The normal state resistivity of Gd-substituted Bi-2223 specimens shows metallic, semiconducting and insulating behaviour. The $T_{mc}(R=0)$ values indicate that (BiPb)-2223 phase is responsible for the observed superconducting transitions in Batch I and Batch II specimens with Gd concentrations $x le 0.7$. This observation is further confirmed in the analysis of XRD patterns of these specimens. Gadolinium, being a magnetic impurity, has pair breaking effect nearudthe Fermi level and decreases $T_{m c}(R=0)$. The analysis of the superconducting fluctuation behaviour (SFB) shows a 2D dimensionality without any cross-over.