(Bi,Pb)-2223相分解-再形成过程中超导相的演变

Study on the Evolution of Superconducting Phases during the Decomposition and Recrystallization of(Bi,Pb)-2223 Phase in the Ag-Sheathed Tape

研究了低氧分压气氛中，不同熔化处理温度下单芯银包套带材（Bi，Pb）-2223（以下称Bi-2223）芯部熔化分解及随后的缓慢冷却阶段，淬火试样中Bi-2223，Bi-2201和Bi-2212相之间的演变关系。结果显示，在Tp=855℃-865℃范围内，随着熔化处理温度（Tp）的升高，淬火带材中Bi-2223相相对含量逐渐减少，而Bi-2201相含量则明显增加。Tp=855℃-860℃时，Bi-2223相发生部分分解，其淬火后的主要产物为Bi-2201，（Sr,Ca）2CuO3（2：1AEC）和（Sr,Ca）14Cu24O41（14：24AEC）。经过随后的缓慢冷却，部分分解的Bi-2223相可以直接从液相中再形成。在所有熔化试样及部分熔化后慢冷所得的试样中均未发现Bi-2212相。当Tp=865℃时，Bi-2223相则全部分解，在同样冷却条件下，其回复过程经历了两个不同的途径，一是少量Bi-2223相直接从液相中生成，二是先从液相中析出Bi-2212相，在随后继续冷却过程中再转变为Bi-2223相。由于Bi-2212转变为Bi-2223所固有的迟缓特性，以致在本实验的冷却条件下，完全分解的Bi-2223相只能部分得到回复。

The evolution relationship among the three well-known superconducting phases in BPSCCO system, Bi-2223, Bi-2201 and Bi-2212, has been investigated after the Bi-2223 core in a Ag-sheathed monofilamentary tape was melted decomposed at different maximun temperatures （Tp）, followed by slow cooling down to the end temperatures in a Ar-7.5%O2 flowing atmosphere. The fractions of Bi-2223 decomposition and Bi-2201 increased with Tp rising from 855℃ to 865 ℃. The decomposition products in the short tapes partially melted at quenched from Tp=855℃-860℃ are Bi-2201, 2：1 AEC and 14：24 AEC etc. During cooling at 0.025℃/min, Bi-2223 phase partially decomposed was fully reformed directly from the melt. No Bi-2212 was found in the specimens which were heated to 855℃-865 ℃ and slowly cooled after melted at 855℃-860℃. The results above mentioned indicate that the Bi-2223 phase can be formed directly from the melt. However, after fully decomposed at 865℃, Bi-2223 phase reformation seems to include two routes at the same cooling rate： a small quantity of this phase recrystallizes from the melt; Bi-2223 is transfered from Bi-2212 which firstly formed from the melt during the subsequent slow-cooling.