Bi-Sr-Ca-Cu-O系氧化物熔体的凝固产物及其向超导体的转变

SOLIDIFIED PRODUCT FROM Bi-Sr-Ca-Cu-O MELT AND ITS TRANSFORMATION INTO SUPERCONDUCTOR

用不同的熔化方法和后续热处理制备了BSCCO系超导体,研究了冷却速度、退火温度、退火时间和不同熔化方法对相变的影响,运用X射线衍射,光学显微镜,电子探针,差热分析,热重分析,导电性和抗磁性测量等分析了组织、结构和性能,结果表明,名义成分为Bi_2(Sr,Ca)_3Cu_2O_x的熔体在空气中凝固时,Bi_2(Sr,Ca)_3Cu_2O_(8+δ)(简称2212)超导相是较稳定的相;包含Bi_2(Sr,Ca)_2CuO_(6+δ)(简称2201)相的产物是易生成的亚稳相;在急冷条件下生成非晶后两者通过后续热处理可以转变成2212相,最佳退火温度在780-870℃间,非晶相也可转变成2201相,激光浮区熔化法(LFZM)制成的2201相退火后易转变成片状或纤维状的2212相,有利于改善超导相颗粒间的连接。

The Bi_2(Sr, Ca)_3Cu_2O_x system superconductor was prepared by different melt-ing procedures and after treatment. The effects of cooling rate, annealing temperature andtime, as well as melting procedures on phase transformation were investigated. The structureand properties were examined by X-ray diffraction, optical microscopy, EPMA, DTA, TGAand measurements of electric and magnetic properties. When the melt of nominal composition Bi_2(Sr, Ca)_3Cu_2O_x solidified in air, the Bi_2(Sr, Ca)_3Cu_2O_(8+δ)(2212) superconductive phaseis stable, the easily solidified product including Bi_2(Sr, Ca)_2CuO_(6+δ)(2201) phase is metas-table, and another may by amorphous if rapidly quenched. The last two may be transformedinto 2212 phase by after treatment with an optimal annealing temperature ranging 780-870℃. While 2201 phase, prepared by the laser floating zone melting method, may easily betransformed into 2212 phase with layer or filament in shape which is favourable to improvethe links among superconductive grains and critic current density.