Concepedia

Formation of Higher Borides During High-Pressure Synthesis and Sintering of Magnesium Diboride and Their Positive Effect on Pinning and Critical Current Density

T. A. Prikhna, W. Gawalek, Yevhenii Savchuk, Artem Kozyrev, Michael Wendt, V.S. Melnikov, V. Z. Turkevich, Viktor Moshchil, Jan Dellith, Christa Shmidt,

IEEE Transactions on Applied Superconductivity · 2009 · 17 citations · 10 references

DOI

Abstract

Critical current density (j c ) of high-pressure (2 GPa) manufactured MgB 2 -based superconductors depends on the amount and distribution of higher borides (MgB 12 ) in MgB 2 matrix, which in turn are determined by the nature of the initial components first of all B or MgB 2 and the temperature of sintering or synthesis. Ti and Ta additions can improve j c by promoting the higher boride formation via impurity hydrogen absorption, thus preventing MgH 2 detrimental for j c being formed, which possibly increases the MgB 12 nucleation barrier. SiC (0.2-0.8 mum) addition increases j c of MgB 2 , allowing us to get j c = 10 6 A/cm 2 at 20 K in the 1 T field: pinning is increased by SiC and higher boride grains and there is no notable interaction between SiC and MgB 2 . As the synthesis temperature increases from 800 to 1050degC, Ti and SiC additions may affect the oxygen segregation and formation of Mg-B-O inclusions enriched with oxygen as compared to the amount of oxygen in the MgB 2 matrix, which can also promote an increase in pinning. Materials high-pressure synthesized from Mg and B taken in 1:4, 1:6, 1:7, 1:8, 1:10, 1:12, 1:20 ratios were superconductive with T c of about 37 K. High j c (7middot10 4 - 2middot10 4 A/cm 2 in zero field at 10-30 K, respectively) showed materials with the matrix composition near MgB 12 stoichiometry, they have doubled microhardness of MgB 2.