Intensive research work has been carried out in order to develop industrially available HTS REBCO-coated conductors under the NEDO project in Japan. Recently, several groups in the project succeeded in the development of high performance coated conductors. Their characteristic features have been evaluated in terms of mechanical properties and their influence on critical currents. The mechanical properties at RT and 77 K were analyzed on the basis of the rule of mixtures. The force-free strain (Aff) was analytically deduced, which indicates the strain at which the residual stress exerted on the superconducting layer becomes zero. Tensile strain dependence on critical currents could be divided into elastic and brittle regions. The reversible strain limit (Arev) was defined as a strain at which the critical current recovers elastically to the level of 99% Ico. Within the elastic region, the critical current showed a convex strain dependence, which is explained as Ekin’s intrinsic strain effect. The degradation beyond the reversible strain limit was attributed to a fracture of the superconducting layer. As a whole, the present study made clear quantitatively the tensile strain behavior of critical currents and proposed a reasonable definition for the reversible strain limit.

We have developed a reliable fabrication process based on a laser scribing method for multi-filamentary coated conductors with a low alternating current loss. This process consists of shallow laser irradiation and two-step chemical etching. The shallow laser irradiation, which penetrates into only a masking polymer tape and a silver stabilizing layer, suppresses generation of dross that is formed due to melting and hardening of a metal substrate. The two-step chemical etching individually for the stabilizing and the superconducting layers prevents over-etching of the superconducting layer and thus suppresses degradation of the critical current (I c ). By using the developed laser scribing process, we realized an improvement of processing speed and a reduction of I c degradation at the same time. Subsequently, we developed reel-to-reel equipment to apply this process to coated conductors several hundred meters long. We succeeded in fabricating 280 m and 70 m long coated conductors with 5 mm width divided into three and five filaments, respectively. It was confirmed that they had one-third and one-fifth hysteresis loss, respectively, in comparison with that before processing, and high inter-filament resistance, over 0.1 M cm. The typical degradation rates of I c in the developed laser scribing process were less than 20%.

We report resistivity and the Hall effect measurements in the normal and superconducting states of MgB 2 single crystal. The resistivity has been found to be anisotropic with slightly temperature dependent resistivity ratio of about 3.5. The Hall constant, with a magnetic field parallel to the Mg and B sheets is negative in contrast to the hole-like Hall response with a field directed along the c-axis indicating presence of both types of charge carriers and, thus, multi-band electronic structure of MgB 2 . The Hall effect in the mixed state shows no sign change anomaly reproducing the Hall effect behavior in clean limit type-II superconductors.

Superconducting BaFe2(As0.6P0.4)2 (Ba122:P) thin films were fabricated on MgO(100) substrates by a pulsed laser deposition (PLD) method using a second-harmonic Nd:YAG (yttrium aluminum garnet) laser. Structural investigation by means of x-ray diffraction confirmed both c-axis orientation and in-plane alignment, or epitaxial growth on the substrate. The film exhibited Tc(onset) = 26.5 K and Tc(zero) = 24.0 K. High Jc values of 3.5 MA cm−2 at 4.2 K in the self-field and over 1 MA cm−2 at 10 K under 1 T were also obtained. Fabrication of Ba122:P film by Nd:YAG PLD seems to be a promising approach for preparing superconducting tapes, since a high-Tc and high-Jc film can be relatively easily obtained.

No abstract