Thermal Stability of BaK122 Superconducting Bulks in Sealed Conditions

Abstract

The thermal stability of BaK122 is a critical parameter for practical applications, such as in the fabrication of the superconducting joint, the re-sintering of the coil, etc. Therefore, study on the thermal stability of BaK122 at high temperatures is necessary. In this work, thermal stability of the BaK122 superconducting bulks was investigated under various sealed conditions. It is found that significant FeAs impurity is formed on the surface of BaK122 samples sintered at 800 °C, while unknown impurities emerge at 900 °C. Specifically, FeAs is distributed within ∼0.2 mm of the surface for the samples sintered at 900 °C, whereas unknown phases are within ∼0.1 mm. Increasing the sintering spatial density will suppress surface phase decomposition and obviously improve superconductivity of the samples. The decomposition of BaK122 is primarily induced by K loss. The introduction of elemental K in a sealed environment will effectively restrain surface decomposition and have a moderate impact on superconductivity of BaK122. The mechanisms of BaK122 decomposition in sealed conditions were summarized based on the experiment results.