Effect of malonic acid and of different doping methods on the superconducting properties of MgB2 superconductors

摘要

In this paper, malonic acid was tested as a new carbon source and its effects on the structural and superconducting properties of bulk MgB2 have been systematically investigated. The detailed pyrolysis process of malonic acid was analyzed to understand the possible doping mechanism of malonic acid added MgB2 samples. The weight fraction of MgO phase and the actual carbon substitution level in bulk MgB2 increased with a higher amount of malonic acid addition, which was proven to be mainly caused by the reaction of Mg and CO2 gas. A moderate amount of malonic acid addition resulted in grain refinement and enhanced flux pinning. Bulk MgB2 with 10 wt% malonic acid addition showed much higher J(c) values in the entire magnetic field range. Three different doping methods with the same amount of malonic acid addition were compared. MgB2 samples using malonic acid and ethanol processed boron showed the highest J(c) value, which was 7.2 times larger than that of the pure MgB2 at 20 K and 5 T.