Zn取代Cu抑制YBa2Cu3O7-y超导电性的机理研究

通过精心制备样品,系统地研究分析YBa₂Cu₃O_7-y体系的超导转变、电阻率、热电势、晶体结构,以及氧含量等随Zn浓度变化的规律。并指出,Zn取代Cu导致CuO面上Cu的数目减少,载流子浓度下降;正是以Zn杂质为中心的正常芯及随之产生的渗流性破坏抑制了YBa₂Cu_3-xO_7-y的超导电性;以Zn杂质散射为基础的渗流超导电性模型与实验结果一致。

MECHANISM OF Tc DEPRESSION INDUCED BY Zn SUBSTITUTION FOR Cu IN YBa2Cu3O7-y SYSTEM

The mechanism of T_c suppression induced by Zn substitution for Cu in YBa₂Cu₃O_7-y system has been studied with respect to its electronic transport properties in normal state, superconducting critical temperature, crystal structure, oxygen stoichiometry and so forth. The results show that Zn ion acts as impurity scattering centre, leading to the increase in the resistivity as well as to the anomalous changes of the resistance-temperature relation. In addition , Zn substitution for Cu reduces the carrier concentration due to the reduction of the number of Cu other than the oxidation state in CuO planes, which precludes the band-filling and carrier-over-saturation models for explaining the mechanism of T_c suppression. Semi-quantitative results reveal that each Zn ion present a scattering cross section with a radius larger than the average Cu-O bond length of the CuO planes. This means that a non-superconducting core may appear around each Zn ion. As a result, the superconducting path in CuO plane will be destroyed gradually.as a percolation process. The percolation threshold observed experimentally is consistent with the theoretical calculation. We believe that the emergence of the normal core together with the consequent percolation is the reason why T_c is suppressed so rapidly by Zn substitution for Cu.