Effect of La Doping on Structural and Superconducting Properties of (Bi, Pb)-2223 Ceramics

Abstract

Superconducting ceramics with nominal composition Bi_1.6Pb₀.₄Sr₂Ca_2-yLa_yCu₃O_10+d (0 ≤ y ≤ 0.04); were prepared in pellet form by conventional solid-state reaction method. The samples were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature-dependent resistivity measurements, and AC susceptibility. XRD patterns showed the coexistence of the Bi-2223 and Bi-2212 phases, with all samples exhibiting an orthorhombic structure. With increasing La concentration, the b lattice parameter increased, whereas the c lattice parameter decreased. These changes are consistent with a structural modification associated with La incorporation and may be related to the larger ionic radius of La³⁺ compared with Ca²⁺ and to changes in the oxygen distribution between the CuO₂ and BiO planes. Electrical resistivity measurements showed that the superconducting transition temperature increased up to y = 0.01 and decreased for higher La concentrations, while the residual resistivity increased above y = 0.01, suggesting increased structural or compositional inhomogeneity.