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The discovery of superconductivity at 39 K in MgB 2 has been catching the attention of scientists due to the possibility of applying the material in magnets and electronic devices operating with cryocoolers (temperatures around 20 K). In the present work, a methodology to optimize the critical current densities of this material is described. MgB 2 bulk samples were prepared and analyzed with the addition of other diborides with the same C32 hexagonal structure as MgB 2 (TaB 2 , ZrB 2 , VB 2 , and AlB 2 ) and with simultaneous addition of SiC. Microstructural characterization, performed using SEM+EDS and XRD, was extremely important to determine the distribution and compositional characterization of the superconducting phase. Magnetic superconducting characterization using SQUID was performed to determine the best material addition. As a result we could analyze the behavior of each addition on the current transport capacity, including an analysis of the magnetic flux pinning mechanisms.Index Terms-Addition of diborides and SiC, crystallography, MgB 2 superconductors, microstructure, superconducting properties.

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The optimization of MgB 2 superconducting properties is extremely important for practical application. The introduction of an effective artificial pinning center in this material can enhance its critical current density efficiently. In this paper, VB 2 is described as a material that provides effective pinning in the MgB 2 bulks. The simultaneous addition of SiC as a carbon source is also analyzed. The samples were prepared using ball milling under a controlled atmosphere and heat treatment with a continuous argon flux. As a result, the superconducting properties could be optimized due to the effective improvement in the pinning behavior as well as with the carbon doping.

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This paper describes the synthesis and modification of MgB 2 bulk samples to produce better transport superconducting materials. The methodology uses a mixture of MgB 2 with another diboride, TaB 2 , which has the same C32 hexagonal structure as MgB 2 . The simultaneous addition of TaB 2 and SiC, which contributes carbon doping, is also investigated. As an important result, the critical current densities (J c ) were enhanced at low magnetic fields (0-2 T) when TaB 2 alone was added. In addition, J c was enhanced in the entire range of the measured applied magnetic fields when TaB 2 was simultaneously added with SiC. Some explanations for this J c enhancement are presented.

The relatively high critical temperature and upper critical field and the low cost of the raw materials are the main reasons to consider MgB 2 as a very promising material for superconducting applications. Improving the relatively low flux pinning in this material is important to optimize the critical current density of MgB 2 superconducting wires, tape, and bulks. Adding secondary phases in a controlled way can create new pinning centers and improve the critical current density. This paper describes a methodology to produce MgB 2 powders containing additions of diborides (VB 2 ) and carbon (carbon nanotubes) that can also improve the upper critical field. MgB 2 powders with these additions were used to produce Cu-Nb-MgB 2 and CuNi-Nb-MgB 2 multifilamentary wires. Characterization of the samples showed the microstructure, phase distribution, and microhardness in their cross sections after mechanical deformation, along with some superconducting properties and characteristics.