Substitution effect of Sr2+ by Ca2+ on structure and superconducting properties of Bi2Sr1.6La0.4CuO6+δ (Bi-2201) ceramics

Highlights: • Iso-valence substitution of Ca²⁺ for Sr²⁺ in Bi₂Sr_1.6-xCaxLa_0.4CuO_6+δ leads to the appearance of the high temperature transition. • It improves the bulk onset critical transition temperature, the transition width and the residual resistivity. • The best results for the activation energy of vortices and the irreversibility field are seen for x = 0.4 of Ca content. - Abstract: In this work, the effect of Ca²⁺ iso-valence substitution for Sr²⁺ on properties of Bi₂Sr_1.6La_0.4CuO_6+δ superconductors is presented. Samples series with nominal composition of Bi₂Sr_1.6-xCa_xLa_0.4CuO_6+δ (x= 0, 0.2, 0.4, 0.6 and 0.8) are prepared by a solid-state reaction method. When Ca content is increased, the X-ray diffraction technique shows that the cell parameters a and c decrease, while b one is almost constant. The scanning electron microscopy analysis reveals that the substitution has no significant effect on the porosity and the grain size of the samples. The physical properties of the samples are studied by the analysis of the magneto-resistivity curves measured under magnetic fields in the range 0-1 T. As Ca is added, the results show that the high temperature transition appears and is pushed up to 94.87 K for x=0.8. The substitution also improves the bulk onset critical transition temperature, the transition width, the residual resistivity, the activation energy of vortices and the irreversibility field. The best results are seen for x=0.4 of Ca content.