No abstract

Different boron powders were used for MgB 2 wires manufactured by internal magnesium diffusion. The structure of the MgB 2 core, critical temperature and critical currents of Cu/Ti sheathed wires differing only in boron powder were analyzed and compared. It was found that the particle size and purity of boron powders influence the creation of the MgB 2 phase and, consequently, also considerably influence its superconducting properties. The highest critical current density in the low external field was measured for wire with a boron purity of 98.5% produced by Pavezyum. It was used also for stabilized multi-core MgB 2 wire with high engineering current densities in low magnetic fields at 20 K, which may be attractive for some low field applications, e.g. high-power wind generators.

No abstract

Pulsed-laser deposition of smooth high-Tc superconducting films almost free from droplets and precipitates with the use of velocity filtration of plasma particles is reported. We have removed droplets from laser-induced plasma by using a shutter technique; a reduction of the droplet density by a factor of 105 has been achieved. We have applied the technique to the preparation of high quality YBa2Cu3O7−δ films on (100)-oriented SrTiO3, MgO, Y2O3-stabilized ZrO2 (YSZ) substrates and, furthermore, on (11̄02)-oriented sapphire covered with (100) sublayers of Si and (100) YSZ buffer layers.

MgB2 wires doped with carbon and SiO2 nanoparticles prepared by the modified internal magnesium diffusion method were studied and compared with an undoped reference sample. It was found that doping of boron powder has a substantial effect on the diffusion reaction and that carbon acts as a MgB2 growth suppressor. The highest critical current density exhibited the wire with SMI+C boron powder heat-treated at 650°C/1 h, with almost 10000 Acm -2 at 10 T and 4.2 K. From the point of view of pinning behavior, this wire showed the lowest pinning energies, indicating that high Jc is due to an increased number of pinning sites. The other C-doped wire with the PVZ+C boron powder showed field direction dependent pinning energies with higher energies for the parallel direction, in good agreement with the Jc-results. The SiO2-doped wires exhibited a wide flux jump region and a quickly declining field dependence of Jc.