Effect of annealing on the superconducting properties of Bi_1.7Pb_0.3Sr₂Ca_1-xSm_xCu₂O_y (0.0 ≤ x ≤ 1.0) system

Detailed studies on the superconducting properties of Bi_1.7Pb_0.3Sr₂Ca_1-xSm_xCu₂O_y (0.0 ≤ x ≤ 1.0) system have been done employing X-ray diffraction, electrical resistance, a.c. susceptibility, and d.c. magnetization techniques. XRD data has shown that the a-parameter increases while the c-parameter decreases gradually with increasing Sm concentration (x). Superconducting onsets from a.c. susceptibility measurements have increased with x up to 0.06 and men decreased with Sm content. Magnetization measurements indicated a decrease in superconducting volume ( dM dH) with x. The results have shown that substitution of Ca²⁺ by Sm³⁺ probably brings about changes in the hole carrier concentration, which in turn alters T_c and the volume fraction of the superconducting phase. Vacuum annealing has shown to improve the onsets of T_c although subsequent air annealing has lowered them. The results are explained on the basis of changes in the oxygen content and the average oxidation state of Cu. We have thus shown that the substitution of Sm³⁺ for Ca²⁺ with specific combinations of annealing conditions leads to the optimization of the oxidation state of Cu and, in turn, of T_c.