非原位MgB_2/Fe单芯超导带相成分及其不均匀性

Phases and inhomogeneity in ex-situ PIT MgB_2/Fe monofilamentary tapes

采用非原位粉末套管法制备MgB2/Fe单芯超导带,并通过X射线衍射拟合分析、差热分析对退火前后的MgB2/Fe带超导芯进行了相成分及不均匀性研究。结果表明:所有的超导芯中均含有一定量的MgO,在高温退火样品中靠近铁套管处MgO含量最多;在MgB2超导芯内部检测到少量的MgB4,这是由MgB2分解所得;在MgB2/Fe之间的界面处存在反应层Fe2B,该相是由Fe23B6分解所得到的。MgB2超导芯与铁套管之间的反应以及超导芯中氧的存在限制了这种非原位法制备的MgB2/Fe带中超导相的含量、纯度和均匀性。

The monofilamentary MgB2/Fe superconducting tapes were fabricated by an ex-situ PIT method. The quantitative phase analysis was carried out using X-ray diffraction and differential thermal analysis on short samples heattreated at 700, 850 and 920℃ in vacuum, respectively. The reaction mechanism of MgB2 core during the process of the heat treatment was discussed. The impurity phase of MgO was found in all MgB2 cores and the largest amount was detected near the Fe sheath of the sample annealed at the highest temperature. MgB4 appeares in the inner part of MgB2 core, which is possibly formed by the decomposition of MgB2. A reaction layer （Fe2B） is observed between MgB2 core and Fe sheath, which is decomposed by Fe23P6. The result indicates that the presence of the oxygen inside sheath material is the main obstacle to the further improvement of the phase purity and homogeneity of the ex-situ PIT MgB2/Fe tapes.