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Register a new userSuperconductivity of powder-in-tube LaO0.9F0.1FeAs wires
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We demonstrate that Fe sheathed LaO0.9F0.1FeAs wires with Ti as a buffer layer were successfully fabricated by the powder-in-tube (PIT) method. Comparing to the common two-step vacuum quartz tube synthesis method, the PIT method is more convenient and safe for synthesizing the novel iron-based layered superconductors. Structural analysis by mean of x-ray diffraction shows that the main phase of LaO0.9F0.1FeAs was obtained by this synthesis method. The transition temperature of the LaO0.9F0.1FeAs wire is around 25 K. The micrograph shows a homogeneous microstructure with a grain size of 1-3 micrometers. The results suggest that the PIT process is promising in preparing high-quality iron-based layered superconductor wires.
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The critical current density (Jc) of hot isostatic pressed (HIPed) MgB2 wires, measured by d.c. transport and magnetization, is compared with that of similar wires annealed at ambient pressure. The HIPed wires have a higher Jc than the annealed wires, especially at high temperatures and magnetic fields, and higher irreversibility field (Hirr). The HIPed wires are promising for applications, with Jc>106 A/cm2 at 5 K and zero field and >104 A/cm2 at 1.5 T and 26.5 K, and Hirr ~ 17 T at 4 K. The improvement is attributed to a high density of structural defects, which are the likely source of vortex pinning. These defects, observed by transmission electron microscopy, include small angle twisting, tilting, and bending boundaries, resulting in the formation of sub-grains within MgB2 crystallites.
The high upper critical field and low anisotropy of iron-based superconductors make them being particularly attractive for high-field applications. However, the current carrying capability needs to be enhanced by overcoming the weak-link effect between misaligned grains inside wire and tape conductors. Here we demonstrate a high transport critical current density (Jc) reaching 1.5x10^5 A/cm^2 (Ic = 437 A) at 4.2 K and 10 T in Ba0.6K0.4Fe2As2 (Ba-122) tapes prepared by a combination of conventional powder-in-tube method and optimized hot-press technique. The transport Jc measured at 4.2 K under high magnetic fields of 27 T is still on the level of 5.5x10^4 A/cm^2, which is much higher than those of low-temperature superconductors. This is the first report of hot-pressed Ba-122 superconducting tapes and these Jc values are by far the highest ever reported for iron-based superconducting wires and tapes. These high-performance tapes exhibit high degree of c-axis texture of Ba-122 grains and low anisotropy of transport Jc, showing great potential for construction of high-field superconducting magnets.
We demonstrate that Ta sheathed SmO1-xFxFeAs wires were successfully fabricated by the powder-in-tube (PIT) method for the first time. Structural analysis by mean of x-ray diffraction shows that the main phase of SmO1-xFxFeAs was obtained by this synthesis method. The transition temperature of the SmO0.65F0.35FeAs wires was confirmed to be as high as 52 K. Based on magnetization measurements, it is found that a globe current can flow on macroscopic sample dimensions with Jc of ~3.9x10^3 A/cm^2 at 5 K and self field, while a high Jc about 2x10^5 A/cm^2 is observed within the grains, suggesting that a significant improvement in the globle Jc is possible. It should be noted that the Jc exhibits a very weak field dependence behavior. Furthermore, the upper critical fields (Hc2) determined according to the Werthamer-Helfand-Hohenberg formula are (T= 0 K) = 120 T, indicating a very encouraging application of the new superconductors.
$MgB_2$ becomes superconducting just below 40 K. Whereas porous polycrystalline samples of $MgB_2$ can be synthesized from boron powders, in this letter we demonstrate that dense wires of $MgB_2$ can be prepared by exposing boron filaments to $Mg$ vapor. The resulting wires have a diameter of 160 ${mu}m$, are better than 80% dense and manifest the full $chi = -1/4{pi}$ shielding in the superconducting state. Temperature-dependent resistivity measurements indicate that $MgB_2$ is a highly conducting metal in the normal state with $rho (40 K)$ = 0.38 $mu Ohm$-$cm$. Using this value, an electronic mean free path, $l approx 600~AA$ can be estimated, indicating that $MgB_2$ wires are well within the clean limit. $T_c$, $H_{c2}(T)$, and $J_c$ data indicate that $MgB_2$ manifests comparable or better superconducting properties in dense wire form than it manifests as a sintered pellet.
We report the fabrication of ErAl2 magnetocaloric wires by a powder-in-tube method (PIT) and the evaluation of magnetic entropy change through magnetization measurements. The magnetic entropy change of ErAl2 PIT wires exhibits similar behavior to the bulk counterpart, while its magnitude is reduced by the decrease in the volume fraction of ErAl2 due to the surrounding non-magnetic sheaths. We find that another effect reduces the magnetic entropy change of the ErAl2 PIT wires around the Curie temperature, and discuss its possible origin in terms of a correlation between magnetic properties of ErAl2 and mechanical properties of sheath material.
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