Role of Cerium Addition on Structural and Superconducting Properties of Bi-2212 System

Abstract

This study examines the significant changes in the structural and superconducting properties of cerium (Ce) doped Bi-2212 superconductors via X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), electron dispersive X-ray (EDX), electrical resistance and transport critical current density (Jc) measurements. Ce concentration is varied from x=0.0 until 0.1 in a general stoichiometry of Bi1.8Sr2.0CexCa1.1Cu2.1Oy. Zero resistivity transition temperatures (\(T_{c}^{\mathrm{offset}}\)) of the samples produced by the conventional solid-state reaction method are deduced from the dc resistivity measurements. Furthermore, the phase fractions and lattice parameters are determined from XRD measurements when the microstructure, surface morphology and element composition analyses of the samples are investigated by SEM and EDX measurements, respectively. The results show that \(T_{c}^{\mathrm{offset}}\) and Jc at self-field of the samples reduced gradually with the increase in the Ce addition. Maximum \(T_{c}^{\mathrm{offset}}\) of 79.7 K and Jc of 356.8 A⋅cm−2 at 77 K are obtained for pure sample as against 44.6 K and 18.7 A⋅cm−2, respectively, for the sample doped with 0.1 wt.% Ce. According to the refinement of cell parameters done by considering the structural modulation, the Ce doping is confirmed by both an increase of the lattice parameter a and a decrease of the cell parameter c of the samples in comparison with that of the pure sample. As for SEM measurements, it is found that not only do the surface morphology and grain connectivity degrade but the grain size of the samples also decreases with the increase of the Ce addition. Moreover, EDX images indicate that the elements used for the preparation of samples distribute homogeneously and the Ce atoms enter into the crystal structure by replacing Cu atom. In addition, the variation of ΔTc (\(T_{c}^{\mathrm{onset}} -T_{c}^{\mathrm{offset}}\)) is investigated for the presence of impurities and weak links between superconducting grains of the samples. The possible reasons for the degradation in microstructural and superconducting properties are also interpreted.