Ag_2O对YBa_2Cu_3O_(7-δ)超导性能的影响

EFFECT OF Ag_2O ON SUPERCONDUCTING PROPERTIES OF YBa_2Cu_3O_(7-δ)

掺Ag并通过1050℃高温烧结能明显改善YBCO块状超导体的临界电流密度J_c。横截面为1mm^2的典型样品,J_c为1663A/cm^2(77K,0T)。J_c和场强的关系曲线及不同磁场下测得的交流磁化率表明,晶粒间的耦合增强了。X射线衍射谱表明:123相晶格常数基本未变且保持其正交结构,同时也观察到一些Ag的衍射峰。显然Ag没有进入123晶格内,而只是以一种分散的单质相存在。对掺Ag量高并经过烧结的片状样品,我们发现,在样品的表面深约5C～200μ的范围内,Ag的损失相当严重。对于多数高J_c样品来说,局部熔融织构的分布也较广,但它们完全受样品的制作条件所控制。掺Ag之所以能改善J_c是由于晶间耦合增强及接触电阻降低的结果。

Ag doping comlined with high temperature (1050℃) sintering was found to improve Jc of bulk YBCO markedly. Jc (77K,0T) was 1663A/cm2 for a typical sample with a cross section of 1mm2. Field dependence of Jc and ac surceptibility measurements made at different fields showed that the intergranular coupling had been strengthened. Powder X-ray diffraction showed that the 123 lattice remains orthorhomlic with essentially unchanged lattice parameters. Some diffraction peaks belonging to elemental silver were also detected. Evidently silver doesn't incorporate into the 123 lattice, but rather, stays as a discrete elemental phase. The sintered high-leveldoped pellets ware observed to be depleted of silver within a depth of 50-200μ at both the top and bottom surfaces, Local melted texture was extensive for most high Jc samples but this was observed to be governed completely by preparation conditions, It was therefore suggested that the improved Jc brought about by Ag doping is a consequence of stiengthened intergranular coupling and lowered contact resistivity.