High-Pressure Synthesis of MgB2-Based Material with High Critical Currents

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

“…2(f)-2(h)) contains SiC grains, higher borides and Mg-B-O inclusions, which can be relevant pinning centers. With addition of 20-30 nm and 200-400 nm SiC was formed: the higher was the amount of the lower was [11], especially at 25-35 K (that can be due to carbon penetration into lattice promoting decrease). The reactivity of SiC with coarser grains seemed to be lower and no notable interaction of SiC and (Fig.…”

“…The higher is the amount of these inclusions, the finer they are, and more homogeneously distributed, the higher is the [10]. Up to now our attempts to improve of HP-HT-synthesized by adding SiC with grains of sizes 20-30 and 200-400 nm were unsuccessful: at 10-35 K decreased or remained unchanged [11]. Here our new results of complex study of HP-HT manufacturing of and higher borides using several types of initial boron and powders with and without adding of SiC (200-800 nm), Ti, and Ta, and the regularities of variations of and pining are discussed.…”

High Pressure Synthesized Magnesium Diboride- and Dodecaboride-Based Superconductors: Structure and Properties

“…We succeeded in increasing j c of MgB 2 at 10-25 K by adding 200-800 nm SiC and got highest j c using B(I) in low and middle magnetic fields >10 6 A/cm 2 up to 2 and 1 T and >10 5 A/cm 2 up to 5 and 3.5 T at 10 and 20 K, respectively. It should be mentioned that when we add SiC of 20-30 nm and 200-400 nm SiC in HPS MgB 2 -based structure Mg 2 Si was formed: the higher was the amount of Mg 2 Si the lower was j c [12], especially at 25-35 K (that can be due to carbon penetration into MgB 2 lattice promoting a T c decrease). The reactivity of SiC with coarser grains seemed to be lower and no notable interaction of SiC and MgB 2 (Figure 2 Unfortunately, not for each type of boron the critical current density can be increased by Ti, Ta, or SiC alloying; in many cases j c decreases or stays unchanged.…”

“…As the synthesis temperature increases from 800 to 1050 o C, Ti, Ta, 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 (7⋅10 4 -2⋅10 4 A/cm 2 in zero field at 10 -30 K, respectively) showed materials with the matrix composition of near-MgB 12 stoichiometry, they have doubled microhardness of MgB 2 . The final conclusion concerning possible superconducting properties of MgB 12 will be made after the TEM study.…”

“…It has been established in our previous study that superconductive properties of MgB 2 depend on the amount, size and distribution of higher borides inclusions (the finer the MgB 12 inclusions and the larger amount of them, the higher j c ) [1]. Besides, it has been shown that additions of Ti, Ta, and Zr can essentially improve j c of high-pressure high-temperature synthesized MgB 2 [2][3][4][5], but we observed absolutely different mechanism of their influence than that proposed for materials synthesized under pressureless conditions. In the case that Ti or Zr is added the improvement in critical current density in materials synthesized at ambient pressure is usually explained by the formation of TiB 2 or ZrB 2 thin layers or inclusions at grain boundaries that increase the number of pinning centers, which is ascribed to a j c improvement caused by doping with these elements [6]..…”