Normal and Superconducting Properties of Bi_1.7Pb_0.30Sr₂Ca_1−xLa_xCu₂O_y Superconductor with 0.00 ≤ x ≤ 0.30

Abstract

We report here normal and superconducting properties of Bi_1.7Pb_0.30Sr₂Ca_1−xLa_xCu₂O_y superconductor with various x values (0.00 ≤ x ≤ 0.30). It is found that the replacement of Ca²⁺ by La³⁺ does not influence the phase purity of the samples, while the orthorhombic distortion, excess oxygen, effective Cu valance, and hole carriers/Cu ions are affected. Further, the doping distance and crystal geometry factor are decreased by La, but the distance between neighboring Cu atoms and the density of excess doping are increased. Furthermore, the DTA graphs show strong endothermic peaks at a temperature of 844.1, 848.03, 850.10, and 857.41 °C for pure and La-doped samples, respectively. The thermogravimetric analysis diagrams displayed a sharp mass loss started at about 800 °C and extended up to 1000 °C for all samples. Although the critical temperature T_c of the samples is decreased by La from 94 K to 83, 63, and 51 K, the critical concentration for quenching superconductivity can be extended above 0.30. Moreover, an inverse linear relation between T_m and T_c, given by T_c (K) = − 2.544 T_m (°C) + 2272.1, is also estimated. On the other hand, the Vickers hardness H_v is increased by La up to 0.30 (H_v α T_m, H_v α (1/T_c)), but it is decreased by the applied load F. The H_v-F characters are divided according to the applied load into two parts: the first at lower loads (0.00–1.962 N) and the second at higher loads (2.942–4.904 N). It is noted that the surface energy, elastic indentation, and resistance pressure are increased by La, but their values at higher loads are generally more than that of lower loads. Our results are discussed in terms of the balance between the hole carriers lost by La³⁺ with that introduced by excess oxygen in the Cu-O₂ planes, which alters the quenching of superconductivity by La³⁺ and highlights the present work.