V. Braccini

Large transport critical currents in unsintered MgB2 superconducting tapes

The powder-in-tube process has been employed to fabricate tape-like conductors with a strong metallic sheath and based on the newly discovered MgB2 superconducting phase. Long superconducting tapes have been prepared by packing reacted MgB2 powders inside pure Ag, Cu, and Ni tubes which are then cold worked by drawing and rolling. Such tapes have shown transport properties as good as bulk MgB2 samples sintered in high pressure and high temperature conditions. At 4.2 K, the highest critical current density of 105 A/cm2 has been achieved on nickel-sheathed single-filament conductors. A direct correlation between the sheath tensile strength and the critical current of the unsintered tape has been observed.

Effects of neutron irradiation on polycrystalline Mg 11 B 2

We studied the influence of the disorder introduced in polycrystalline MgB2 samples by neutron irradiation. To circumvent self shielding effects due to the strong interaction between thermal neutrons and 10B we employed isotopically enriched 11B which contains 40 times less 10B than natural B. The comparison of electrical and structural properties of different series of samples irradiated in different neutron sources, also using Cd shields, allowed us to conclude that, despite the low 10B content, the main damage mechanisms are caused by thermal neutrons, whereas fast neutrons play a minor role. Irradiation leads to an improvement in both upper critical field and critical current density for an exposure level in the range 1-2x1018 cm-2. With increasing fluence the superconducting properties are depressed. An in-depth analysis of the critical field and current density behaviour has been carried out to identify what scattering and pinning mechanisms come into play. Finally the correlation between some characteristic lengths and the transition widths is analysed.

Significant enhancement of irreversibility field in clean-limit bulk MgB2

Low resistivity MgB2 bulk samples annealed in Mg vapor show an increase in irreversibility field μ0H*(T) by a factor of ∼2 in both transport and magnetic measurements. The best sample displayed a magnetic irreversibility field μ0HM*>14 T at 4.2 K and ∼6 T at 20 K. These changes were accompanied by an increase of the 40 K resistivity from 1 to 18 μΩ cm and a lowering of the resistivity ratio from 15 to 3, while the critical temperature Tc decreased by only 1–2 K. These results show that systematic processing changes can make MgB2 attractive for magnet applications.

Neutron irradiation of MgB211: From the enhancement to the suppression of superconducting properties

In this letter, we present the effect of neutron irradiation up to fluences of 1.4×1020cm−2 on the superconducting properties of MgB2. In order to obtain a homogeneously distributed disorder, the experiment was carried out on bulk samples prepared with the B11 isotope. Up to fluences of 1018cm−2, the critical temperature (Tc) is slightly diminished (36K) and the superconducting properties are significantly improved; the upper critical field is increased from 13.5T to 20.3T at 12K and the irreversibility field is doubled at 5K. For the largest neutron fluence, Tc is suppressed down to 9.2K and the superconducting properties come out strongly degraded.

Role of weak uncorrelated pinning introduced by BaZrO3 nanorods at low-temperature in (Y,Gd)Ba2Cu3Ox thin films

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Enhanced flux pinning in neutron irradiated MgB2

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Transport properties of powder-in-tube processed MgB2 tapes

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Highly effective and isotropic pinning in epitaxial Fe(Se,Te) thin films grown on CaF2 substrates

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Two-band effects in the transport properties of MgB2

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A new approach for improving global critical current density in Fe(Se0.5Te0.5) polycrystalline materials

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