Evaluation and control of residual amorphous phases in carbon-doped MgB2 superconductors

•Hydrocarbon doping into MgB2 materials retarded the formation of the main phase.•The doping thus led to an increase in amorphous impurities.•However, the content can be controlled by the optimization of the doping method.•The control of amorphous impurities can lead to enhancement of the transport Jc. [Display omitted] Evaluation and control of amorphous phases in materials are very important for optimizing their properties. Herein, we focus on polycrystalline MgB2 materials prepared with hydrocarbon doping and study the effects of residual amorphous impurities on the superconducting performance. Carbon is known to be an effective element for enhancing the transport critical current under an external magnetic field. The doped samples were prepared under two different nominal conditions, MgB2(C16H10)x/16 and MgB2−x(C16H10)x/16, which respectively correspond to additional and substitutional type doping of the MgB2 composition. Regardless of the doping type, both fabrication methods retarded the formation of the MgB2 phase due to the dopant, leading to an increase in amorphous impurities. However, the apparent phenomena that arise from the additional and substitutional types are still elusive. Ultimately, the structural differences due to the impurity effects caused significant changes in the transport critical current performance. The present quantitative analysis of the amorphous impurities thus paves the way to further optimize the doping methodology for MgB2 superconducting materials.