TaB2 and VB2 addition in the MgB2 superconductor, and co-doping with SiC

L. B. S. DA SILVA; G. SERRANO; A. SERQUIS; V. C. VELLOSO METZNER; E. HELLTROM; D. RODRIGUES JR.

Gramado

Encuentro; X Brazilian MRS Meeting; 2011

SBPMat - Brazil MRS

Extensive researches on doping MgB2 superconductor with different elements have revealed that carbon is an effective element for significant enhancement of the critical current density in high magnetic fields [1]. This enhancement is mainly due to carbon replacing boron in the MgB2 crystal lattice [2]. Following this line, several groups around the world have been investigating different sources of doping. The addition of materials with the AlB2 crystalline structure (as TaB2 and VB2) has not been exhaustively investigated, but some previous works reported the use of TaB2 [3] and ZrB2 [4,5]. In these works the addition of the diborides was efficient, improving the magnetic flux pinning and, consequently, the transport properties of these superconductors. In the present work it is described a methodology to optimize the critical current densities in MgB2 bulk superconductors. The method uses the mixture of the MgB2 superconductor with the TaB2 and VB2 addition, which has the same C32 hexagonal structure as the MgB2, and SiC, that contribute with C, to replace B in the crystalline structure of the matrix. The mechanical mixture of the powders, obtained by ball milling, was important to improve densification and grain boundary connectivity, and has a positive influence on the final crystalline structure, maintaining the hexagonal structure, and generating intragranular and intergranular pinning centers. Microstructural characterizations, performed using SEM and XRD, were extremely important to determine the distribution and compositional characterization of the material. Magnetic superconducting characterization using SQUID was performed and showed an improvement of the critical current densities in low magnetic fields when just the diborides were add in the matrix, while the best values of the critical current densities under high magnetic fields were showed for the samples with addition of SiC and diborides simultaneously.