The superconducting properties of Bi-Pb-Sr-Ca-Cu-O bulk materials rapidly melted and solidified by a CO_2 laser

摘要

Since the discovery of superconducting materials with Tc - 85 K in the Bi-Sr-Ca-Cu-0 system by Maeda et al. [1], many studies have been carried out to improve Tc. This system was found to have three different superconducting phases, namely, a phase with high Tc (2223, Tc = 110K), one with low Tc (2212, Tc = 80 K), and one with very low Tc (2201, Tc = 20 K). However, it is extremely difficult to synthesize single 2223 phase from Bi2Sr2CaCu2O.,, alone. It is well known that the partial substitution of Bi with Pb [2,3] or in reduced oxygen partial pressure [4] during sintering, would result in Bi-Sr-Ca-Cu-0 superconductors with a large amount of the high Tc phase. Our recent work [5] indicated that the high Tc phase in the Bi-Pb-Sr-Ca-Cu-O system could be easily prepared by using a calcining and reheating process. On the other hand, Chen et al. [6] also reported that laser calcination of the Bi-Pb-Sr-Ca-Cu-0 compound indeed enhanced formation kinetics of the high Tc phase. However, the high Tc phase is very difficult to recover from the melting process. In order to better understand the relationship between the recovery and melting process in the Bi-Pb-Sr-Ca-Cu-O system, the work reported here was initiated to study the superconducting properties of Bi-Pb-Sr-Ca-Cu-O bulk materials which were rapidly melted and solidified by a CO2 laser.