Evaluation of Superconducting Properties and Diffusion Behavior of Ex Situ and In Situ Bulk MgB2 Materials with Ni Coating

Abstract

Ex situ and in situ bulk MgB2 superconducting materials have successfully been produced by the simple amorphous boron and nano-amorphous boron powders with the processes of ball milling, pressing, and annealing. The superconducting properties and diffusion behavior of MgB2 samples after nickel (Ni) coating process have been characterized and compared to the microstructure and performance of uncoated (bare) MgB2 bulk sample. One surface of MgB2 superconductor sample was coated with a thin Ni layer of about 50 - 60 mu m thickness using vapor deposition techniques in versatile high vacuum coater, then every sample was annealed at temperatures between 923 and 1123 K for 1 h. The role of annealing temperature on physical, electrical, superconducting, and structural characterizations of bare and Ni-coated ex situ/in situ MgB2 bulk superconductors has been studied using X-ray diffraction and dc electrical resistivity versus temperature measurements. Finally, the Ni diffusion coefficients (D-Ni = D(0)exp(E/k(B)T)) are calculated in the temperature range to calculate the required minimum activation energy value for the Ni atoms/ions into the ex situ MgB2 crystal structure for the first time.