Campbell法研究MgB2晶粒特性与临界电流密度关系

Study on critical current density and microstructure in MgB_2 bulks by Campbell method

用PIT(powder in tube)法在不同条件下制备MgB2样品,通过X射线衍射、扫描电子显微镜(SEM)对不同参数下制备样品的成分和微观结构进行了表征;利用Campbell法检测样品的bac-λ′关系,求得样品的超导临界转变电流密度Jc;由样品的Jc结合形貌与相成分对比分析,结果表明:长时间烧结,晶粒较大,利于导电,但缺乏钉扎作用,在外磁场下超导电流减小。长时间烧结,晶界间氧化层增厚,超导电流密度减小。

MgB2 superconductors were prepared by PIT method under different conditions.The phases and microstructure of the samples were investigated by X-ray diffraction（XRD） and scanning electron microscopy（SEM）.The curves of magnetic flux penetration depth vs.alternating magnetic field（bac vs.λ＇curve） of MgB2 samples were measured by Campbell method,and the samples critical current density in different magnetic fields were obtained.The results show that coarse grains are obtained in MgB2 superconductors sintered for longer time,with is beneficial to electrical conduction,however,the current is reduced in magnetic field for the weaker pinning effect.The oxidation layer at grain boundaries is thicker for the long-time sintered MgB2 bulks,and its superconductor current density is reduced.