The synthesis of lamellar nano MgB2 grains with nanoimpurities, flux pinning centers and their significantly improved critical current density

Abstract

MgB₂ superconductors with unique microstructures were rapidly fabricated at low temperatures, and exhibited significantly improved critical current density (J_c). According to the microstructure observations, the prepared samples consisted of lamellar nano MgB₂ grains with many embedded nanoimpurities (about 10 nm). The formation of these lamellar nano MgB₂ grains is associated with the presence of a local Mg–Cu liquid at sintering temperatures as low as 575 °C. The ball milling treatment of the original powders also plays a positive role in the growth of lamellar grains. Based on an analysis of the relationship between resistivity and temperature, the lamellar nano MgB₂ grains in the prepared sample possess better grain connectivity than the typical morphology of MgB₂ samples prepared by traditional high-temperature sintering. Furthermore, the presence of many nano MgB₂ grain boundaries and nano impurities in the prepared sample can obviously increase the flux pinning centers in accordance with the analysis of flux pinning behavior. Both factors mentioned above contribute to the significant improvement in J_c from low field to relative high field. The method developed in the present work is an effective and low-cost way to further enhance J_c in MgB₂ superconductors across a wide range of applied magnetic fields without using expensive nanometer-sized dopants.