Microstructural analysis of magnesium diboride (MgB2) doped with ZrB2 and TaB2 through high-energy ball milling and heat treatments using hip

Abstract

Among the superconductors that can be used in applications, the MgB2 is considered the high field conductor of the future. The exceptionally high values of critical field (H 40T) and critical temperature (H 35-40K) show that MgB2 is capable of replacing Nb3Sn as the choice for these applications, even due to the low cost of materials and the possibility to use cryogenic refrigerators. The optimization of the magnetic flux pinning in these conductors is of vital importance to improve their critical currents. The introduction of dopings and intragranular or intergranular phases in the superconducting matrix can assist in the efficiency of flux pinning and on the connectivity of the grains, and affect the superconducting phase, changing its resistivity, upper critical field and critical temperature, properties and characteristics of interest for practical applications. A very suitable method for the homogeneous mixture of compounds that can be used in the analysis of doping of superconducting materials, which can be used for scaling up for commercial production, is the high-energy milling. The present project suggests the characterization of samples prepared using this technique aiming the determination of the efficiency of mixing and doping using two different equipments/methods of milling/doping: SPEX and Pulverisette. The MgB2 samples were doped with compounds with AlB2-type crystalline structure, with the same C32 hexagonal structure than MgB2, enabling the maintenance of the structures of phases practically unchanged and the efficient mixture of the superconductor with the dopants. It is suggested that this mixture will positively influence the final crystalline structure, probably maintaining the AlB2 hexagonal structure, and it will generate intragranular and intergranular pinning centers. The results of the characterization can be directly used to define the methodology to prepare MgB2 superconductors in the form of bulks, tapes and wires for technological applications. (AU)