Effect of Sb₂O₃ Addition on the Formation of the Superconductive Phases in Bi-Pb-Sr-Ca-Cu-O System

Specimens of (M_2.1) Sr_2.0Ca_2.0Cu_3.15O_y,[(M_2.1) = (Bi_2.1-m-xPb_mSb_z):0.1≤m<0.5, 0≤z≤0.4)] were sintered at 830, 840 or 850°C for 20hr after pre-treatment (20hr) and heating processes [I (20hr) and II (40hr) using envelope method] at the same temperature in air atmosphere. XRD patterns of specimens in each process and the resistance curves of sintered specimens were compared in order to find effects of Sb₂O₃ addition on the formation of high-Tc phase. The optimum heat treatment temperature was 840°C, which was a little lower than that of specimens without Sb³⁺ (z=0). And the range of treatment temperature forming high-Tc phase becomes narrower. In reaction diagram at 840°C, it was found that high-Tc phase amounted to 70~80% for 20~40hr at the small content of Sb₃₊: z≤0.2, although any single phase of high-Tc was not obtained. For specimen with Sb³⁺ addition, the formation time of high-Tc phase was reduced very much in such composition range. A special case was observed in the specimens with Bi content of 1.75~1.80mol. In the case, Sb³⁺ content incorporated with the ratio of Pb²⁺: Sb³⁺ larger than 8:2 brought a little increase of Tc rather than the decrease of Tc. The composition of the case, for example, is (M_2.1) = (Bi_1.8Pb_0.3-zSb_z) with z=0.05.