固态配料和硝酸盐共沉淀配料制备Bi(Pb)—Sr—Ca—Cu—O系高温超导相的工艺比较

用固态配料和硝酸盐共沉淀配料制备了各组份为(Bi_(1.85)Pb_(0.40))Sr_(1.95)Ca_(2.05)Cu_(8.10)的超导材料,研究了两种不同制备工艺对Bi系超导相形成过程、超导电磁性能和显微结构的影响.实验发现,由共沉淀制备的样品T_(c(zero))稳定性好,T_(c(zero))均在107.5K以上.SEM观察表明:共沉淀法制备的样品中超导相颗粒比固态配料制备的要细小、均匀,颗粒间连结紧密,与T_(c(zero))结果相符.但XRD相分析结果显示:固态配料样品中高温相含量高于共沉淀配料,共沉淀配料制备作品中高、低温相同时存在,但其交流磁化率—温度曲线上仅在120K附近出现相应于高温相的抗磁信号.研究认为,这是由于共沉淀配料烧成时,高温相容易在部分液相参与下,在低温相表面通过反应成核生长,导致在形成的高温相内部包裹有残余低温相的“内芯”.依此包裹模型可自洽地解释X射线相分析与电、磁性能测定结果间的矛盾,讨论了Bi系高温相的形成机理,为选择合理的制备工艺提供了依据.

Technical Comparison for the Formation of Bi(Pb)-Sr-Ca-Cu-O High-T_e Superconductor Prepared by Solid-State Mixture and Nitrate Coprecipitation Mixture

Superconductors of nominal composition (Bi1.85 Pb0.40) Sr1.95 Ca2.05Cu3.10) were prepared by solid-state mixture and nitrate coprecipitation mixture. The effect of two different preparation procedures on the superconductor forming process, electric - magnetic property and microstructure was studied. Coprecipitation sample had a high stability of Tc(zero) which all were higher than 107. 5K.SEM showed that the superconductor grain in the sample prepared by coprecipitation method was small and homogeneous, the jointing between grains was coLse. SEM result was consistent with the result of TC(zero), It was found from XRD results that the volume of high-Tc phase in samples prepared by solid-state method was higher than that in samples prepared by coprecipitation method. In coprecipitation samples the suscetibility measurements showed there was a sharp-drop at 120K which was responed to the high-Tc phase and no presence of low-Tc phase, meanwhile both the high-Tc phase and Low-Tc phase existed in the same samples by XRD result. We consider that when the coprecipitation samples were sintered ,the high-Tc phase was nucleated and grew on the low-Tc phase's surface with participation of partial liquid phase,and the result was that the remaining low-Tc phase was wraped up inside the high-Tc phase. This pattern can expound the contradiction between the result of XRD and the result of the resistivity and susceptibility meansurements. The formation mechanism of high-Tc phase was discussed. These results provided foundation for the reasonable technical procedure.