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Register a new userEnhancement of superconducting properties in FeSe wires using a quenching technique
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Enhancements of superconducting properties were observed in FeSe wires using a quenching technique. Zero resistivity was achieved at about 10 K in quenched wires, which is about 2 K higher than that of polycrystalline FeSe bulk. Furthermore, transport Jc of quenched wires showed three times higher than that of furnace-cooled wires. In contrast, the quenched polycrystalline FeSe bulks did not show the enhancement of Tc. The quenching technique is a greatly promising for fabricating FeSe wires with high Tc and high Jc, and quenched FeSe wires have high potential for superconducting wire applications.
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We have fabricated a series of iron-sheathed superconducting wires prepared by the powder-in-tube technique from (MgB_2)_{1-x}:(Mg+2B)_x initial powder mixtures taken with different proportions, so that x varies from 0 to 1. It turned out that ex-situ prepared wire (x = 0) has considerable disadvantages compared to all the other wires in which in-situ assisted (0 < x < 1) or pure in-situ (x = 1) preparation was used due to weaker inter-grain connectivity. As a result, higher critical current densities J_c were measured over the entire range of applied magnetic fields B_a for all the samples with x > 0. Pinning of vortices in MgB_2 wires is shown to be due to grain boundaries. J_c(B_a) behavior is governed by an interplay between the transparency of grain boundaries and the amount of pinning grain boundaries. Differences between thermo-magnetic flux-jump instabilities in the samples and a possible threat to practical applications are also discussed.
In this study, we investigated the gate voltage dependence of $T_{mathrm c}$ in electrochemically etched FeSe films with an electric-double layer transistor structure. The $T_{mathrm c}^{mathrm {zero}}$ value of the etched FeSe films with a lower gate voltage ($V_{mathrm g}$ = 2.5 and 3.3 V) reaches 46 K, which is the highest value among almost all reported values from the resistivity measurements except for the data by Ge et al. This enhanced $T_{mathrm c}$ remains unchanged even after the discharge process, unlike the results for electrostatic doping without an etching process. Our results suggest that the origin of the increase in $T_{mathrm c}$ is not electrostatic doping but rather the electrochemical reaction at the surface of an etched films.
We investigated the influence of different Ag additions (up to 10 wt %) on the superconducting properties of FeSe0.94. The structural investigations (XRD and SEM) indicated that Ag is present in three different forms. Ag at grain boundaries supports the excellent intergrain connections and reduces superconducting transition width to values smaller than 1K at B=0 and smaller than 2.74 K at B=14 T. Ag insertion in the crystal lattice unit cell provides additional carriers and changes the electron hole imbalance in FeSe0.94. This results in an increase in the magnetoresistive effect (MR) and critical temperature (Tc). Reacted Ag forms a small amount (~1%) of Ag2Se impurity phase, which may increase the pinning energy in comparison with that of the undoped sample. The enhanced upper critical field (Bc2) is also a result of the increased impurity scattering. Thus, unlike cuprates Ag addition enhances the Tc, Bc2, pinning energy and MR making the properties of polycrystalline FeSe0.94 similar to those of single crystals.
Synthesis, electrical and magnetic characterization of superconducting FeSe0.85 compound is reported. An anomaly in the magnetization against temperature around 90K is observed. Magnetic characterization of a commercial compound with nominal FeSe stoichiometry is also presented. The overall magnetic behaviors as well as the magnetic anomaly in both compounds are discussed in terms of magnetic impurities and secondary phases. Keyword: A. Superconductors
In DC and AC practical applications of MgB2 superconducting wires an important role is represented by the material sheath which has to provide, among other things, a suitable electrical and thermal stabilization. A way to obtain a large enough amount of low resistivity material in to the conductor architecture is to use it as external sheath. In this paper we study ex-situ multifilamentary MgB2 wires using oxide-dispersion-strengthened copper (GlidCop) as external sheath in order to reach a good compromise between critical current density and thermal properties. We prepared three GlidCop samples differing by the content of dispersed sub-microscopic Al2O3 particles. We characterized the superconducting and thermal properties and we showed that the good thermal conductivity together the good mechanical properties and a reasonable critical current density make of GlidCop composite wire a useful conductor for applications where high thermal conductivity is request at temperature above 30K, such as Superconducting-FCL.
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