| dc.description |
The effect of doping with Ti, Ta, SiC in complex with synthesis temperature on the amount and distribution of structural inhomogeneities in MgB<sub>2</sub> matrix of high-pressure-synthesized-materials (2 GPa) which can influence pinning: higher borides (MgB<sub>12</sub>) and oxygen-enriched Mg-B-O inclusions, was established and a mechanism of doping effect on j<sub>c</sub> increase different from the generally accepted was proposed. Near theoretically dense SiC-doped material exhibited j<sub>c</sub>= 10<sup>6</sup> A/cm<sup>2</sup> in 1T field and H<sub>irr</sub> =8.5 T at 20 K. The highest jc in fields above 9, 6, and 4 T at 10, 20, and 25 K, respectively, was demonstrated by materials synthesized at 2 GPa, 600 °C from Mg and B without additions (at 20 K j<sub>c</sub>= 10<sup>2</sup> A/cm<sup>2</sup> in 10 T field). Materials synthesized from Mg and B taken up to 1:20 ratio were superconductive. The highest j<sub>c</sub> (6×10<sup>4</sup> A/cm<sup>2</sup> at 20 K in zero field, H<sub>irr</sub>= 5 T) and the amount of SC phase (95.3% of shielding fraction), T<sub>c</sub> being 37 K were demonstrated by materials having near MgB<sub>12</sub> composition of the matrix. The materials with MgB<sub>12</sub> matrix had a doubled microhardness of that with MgB<sub>2</sub> matrix (25±1.1 GPa and 13.08±1.07 GPa, at a load of 4.9 N, respectively). |
