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SmBa2Cu3O7 (SmBCO) coated conductors were grown on IBAD-MgO templates the evaporation using a drum-in-dual-chambers (EDDC) deposition system. The material showed a critical temperature of 93 \sim 94 K and a critical current of 200 \sim 250 A/cm-width at 77 K in a self-field. The current-limiting properties and local structure of the films were examined by laser-induced thermoelectric (LITE) imaging and low temperature laser scanning microscopy (LTLSM). Surface morphology and chemical composition of the superconducting layers were examined by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), respectively. A 100\ \mum\times 1\ mm-microbridge was fabricated using a photolithographic technique and etching process. The measured LITE images of the SmBCO coated conductor showed that some grains on the surface, surface inhomogeneity, second phases, defects and tilted grains, cause different thermal gradients. The LTLSM images revealed two dimensional variations of local flux flow on the films as a function of the local critical current. The findings are consistent with the LITE images, indicating that both methods can visualize the local structures and phases. [ABSTRACT FROM AUTHOR]

Abstract: We have investigated the improvement of critical current in YBCO coated conductors in association with c-axis correlated artificial pinning centers (APCs). Current carrying property has been measured in detail at various conditions of temperature, T: 65–83K, magnetic field, B: self-field to 17T, and field’s angles, θ. The APCs were introduced by pulse laser deposition process using 2vol% YSZ doped target. The enhancement of J c in parallel field along the c-axis direction was observed experimentally over wide range T, B, and θ. Moreover, improvements of transition field and pinning force density in B∥c were also evaluated by pinning analysis based on percolation model. [Copyright &y& Elsevier]

Abstract: We investigated the local inhomogeneity of flux flow dissipation by use of low temperature scanning laser microscopy (LTSLM) in a Y1Ba2Cu3O7−δ (YBCO) coated conductor obtained by the Metal-Organic Deposition process using metal trifuluoroacetate (TFA-MOD process). The LTSLM images showed that the highest J c value in local region reached almost two times higher than the minimum value, while the global J c was limited by the weakest spot. Typical length scale of the spatial inhomogeneity of J c was about several tens to hundreds μm. [Copyright &y& Elsevier]

The author’s recent studies on the critical current properties in Bi-2223 multifilamentary tapes as well as YBCO coated IBAD tapes have been reviewed. Extended electric field vs. current density (E–J) characteristics were studied over wide range of temperature, T, magnetic field, B, and angle, θ. Based on the analysis of statistic Jc distribution and scaling, we derived an analytical expression for J as a function of E, T, B, and θ. This method allows us to describe and extrapolate the nonlinear E–J characteristics even in extremely low E region and/or high B region based on rather simple measurements. [Copyright &y& Elsevier]

Critical current properties in a YBCO coated tape have been studied as a function of temperature, magnetic field and field angle under high magnetic field up to 18 T. 1 μm thick YBCO film was deposited on a bi-axially aligned Y2O3/YSZ/Hastelloy substrate fabricated by the IBAD technique. The value of critical current, Ic, of the 1 cm wide tape reached as high as 85 A at 77 K in self-field condition. After etching the tape into 100 μm wide and 1 mm long bridge, we measured extended E–J characteristics. The value of critical current density, Jc, is maintained higher than 105 A/cm2 at 70 K in 5 T perpendicular to the tape surface. Moreover, the power index n and the so called glass–liquid transition field, BGL, of the tape in perpendicular field are superior to those of epitaxial film deposited on a SrTiO3 single crystalline substrate. Jc vs. angle relationship shows broad peak around 90° where field is perpendicular to the tape surface, in addition to a sharp peak at 0°. These results suggest that the tape is highly uniform and correlated defects along c-axis direction contribute to flux pinning. [Copyright &y& Elsevier]

We have investigated the influence of sample width on the transport properties in YBCO thin film using 10, 120, and 1200 μm-wide bridges formed in a same c-axis oriented YBCO film deposited on a SrTiO3 substrate. We measured I–V characteristics of the bridges at various temperature, T, and magnetic field, B, perpendicular to the film surface. It has been found that the so called glass–liquid transition field, BGL, reduces as the sample width becomes narrower, while the critical temperature, Tc, and critical current density, Jc, in the glass region (B) are almost independent of the width of the bridges. The good agreement of Tc and Jc in three bridges indicates high uniformity of the bridges and that the reduction of BGL does not come from the degradation of the film. The measured width dependence of BGL can be scaled with a constant critical index as can be predicted by the percolation model at all measured temperature region from 70 to 85 K. The influence of sample width on Jc has also been discussed based on the scaling analysis. [Copyright &y& Elsevier]

Current transport properties in YBCO coated ion beam assisted deposition tapes have been studied as a function of temperature, magnetic field and field angle under high magnetic fields up to 18 T. The value of critical current, Ic, for 1 cm wide tape was 85 A at 77.3 K in self-field. Detailed properties of critical current density, Jc, were studied using 100 μm wide and 1 mm long bridge patterned in the tape. The results were compared with the properties of epitaxial YBCO thin films deposited on SrTiO3 single crystalline substrate. The value of critical current density, Jc, was maintained higher than 105 A/cm2 at 70 K in 5 T perpendicular to the tape surface. The value is ≈1/4 of Jc value in epitaxial thin film. In higher magnetic field, the difference becomes smaller. Power E–J relationship was observed over wide range of temperature and magnetic field. The power index n were superior to those of epitaxial thin films. And, the so-called glass–liquid transition field, BGL, of the coated tape was also superior to that of epitaxial thin films. Angle dependences of Jc showed a broad peak around 90° (∥c), in addition to a sharp peak at 0° (⊥c). These results suggest that correlated defects along c-axis direction contribute as pinning sites. [Copyright &y& Elsevier]

We have studied electrical properties of YBCO/Y/sub 0.7/Ca/sub 0.3/Ba/sub 2/Cu/sub 3/O/sub 7-x/ (Ca-YBCO)/YBCO trilayer junctions using c-axis oriented films. The Ca-YBCO films used here are the overdoped version of YBCO and show transition temperatures around 55 K. All of the junctions show RSJ-like current-voltage characteristics in a certain temperature range, though the range decreases with the Ca-YBCO interlayer thickness. For an applied magnetic field, the junctions show Fraunhofer pattern, indicating a Josephson coupling through the interlayers. The normal resistance of the junctions is proportional to the thickness of the interlayer, suggesting little interface resistance. The exponential dependence of the critical current on temperature and that on the interlayer thickness mean that the junctions behave as SNS junctions. These experimental results imply the proximity effect along c-axis in high temperature superconductors. [ABSTRACT FROM PUBLISHER]

Abstract: We have investigated current transport property in Gd1Ba2Cu3O7− δ coated conductor with artificial pinning centers in a wide range of temperature, magnetic field, B up to 27T, and field angle. Due to the additional c-axis correlated pins, critical current density, J c in B//c was enhanced and the improvement was observed in wide range of B. On the other hand, around B⊥c below 65K, the angular dependence of n-value showed a valley-like behavior, although the J c was increasing. In addition, the temperature dependence of the pinning force density defined as J c × B was not scaled on an expected master curve. These results indicate the pinning in B⊥c is governed by different mechanism below 65K and high magnetic field. [ABSTRACT FROM AUTHOR]

Abstract: We have investigated critical current property in YBa2Cu3O7− δ (YBCO) coated conductor fabricated by improved metal organic deposition using trifluoroacetates (TFA–MOD) process optimizing conditions such as solution compositions. The electric field vs. current density (E–J) characteristic measurement was carried out at wide range of temperature, T, and magnetic field, B. Critical current density, J c, reached 3.8×1010 A/m2 at 77K in self-field for 1.2μm thick YBCO layer. In-field J c is also improved by this new process. From the analysis of E–J characteristics, we have found out that the shape of statistical distribution of J c in the new process becomes sharper than that of the previous one. These results indicate that the uniformity of YBCO layer is improved by the new process. Furthermore, analytical expression of E–J characteristics, which is based on a percolation model and a scaling law of the pinning force density, shows good agreement with the experimental results. This allows us to predict the critical current property at arbitrary conditions of T and B even if we couldnot have measured data. For example, it is predicted that J c could be about 1×1010 A/m2 at 4.2K and 30T parallel to the c-axis. [Copyright &y& Elsevier]

Abstract: We have visualized non-uniform current flow in RE123 coated conductors by using a scanning Hall-probe magnetic microscopy (SHPM). Newly developed SHPM system allows us to measure two-dimensional magnetic field distribution with high spatial resolution in micro-meter scale. Corresponding current density distribution can be obtained from the magnetic field image by solving inverted Biot–Savart’s law. One of the most important advantages of the present system is to visualize the current density distribution in practical high transport current and also in wide scanning area. For example, the system has current leads with large capacity up to 500A, and the operating distance can be 15cm by 15cm with a micro-meter step distance. Using the SHPM system, we have successfully visualized current density distributions in the coated conductor, and clarified different kinds of non-uniform current flow. Those insights are very useful to identify local defects as well as non-uniform tape quality. These results indicate that the SHPM system is a powerful diagnostic tool not only to observe spatial inhomogeneities of transport property but also to understand their reason in practical coated conductors. [Copyright &y& Elsevier]

Abstract: Prior to the development of fabrication technique for the chemical vapor deposited (CVD) YBa2Cu3O7-δ coated conductor on a IBAD-Gd2Zr2O7, investigations on the improvement of spatial homogeneity have been done. By using spatially resolved measurements and combined multiple microanalysis techniques with length scale of several μm, physical and transport properties of the CVD samples have been investigated before and after fabrication modification. Structural inhomogeneity was visualized using thermoelectric voltage imaging (TVI) technique using a laser scanning microscope. Laser scanning microscopy at superconducting temperature is used to visualize flux flow dissipation; furthermore, mappings of 2D local current flow density distribution have been done using a scanning SQUID microscopy. It has been shown that the superconducting layer consisted of YBCO matrix with localized defects originating from the buffer layer. This led to current non-uniformity and caused high flux flow dissipation within the vicinity of the defects. Process conditions have been modified effectively based on those insights. After fabrication modification, our measurement analyses shows that the texturing of the YBCO layer improved significantly and the appearance of spatially distributed obstacles that are responsible for non-uniform current distribution and localized dissipation are reduced. Our complementing, quick yet non-invasive technique not only can quantify the improvement of YBCO homogeneity but also shed light on the basic understanding of the current limiting mechanism in the IBAD based coated conductors. [Copyright &y& Elsevier]

Abstract: Critical current (I c) of a Bi-2223 tape fabricated by controlled-overpressure (CT-OP) sintering method has been attained up to 200 A-class in recent years. However, current limiting factors have not been fully clarified yet. In this study, we have investigated local current distributions in a CT-OP Bi-2223 tape by using the scanning Hall probe magnetic microscopy. As a result, it has been found that large sheet current flows in the center of the sample. Even though the influence of self-field is taken into account, there is a clear difference of local I c across the width. The maximum sheet current value in the center of the tape is 400–450A/cm when we applied the bias current of 100A, which is equal to the I c at around 87K. This value is equivalent to 800–900A/cm at 77K taking into account the value of I c. Furthermore, such current distribution continues uniformly in length direction. From these results, we have concluded that improvement of current uniformity across the tape width is the effective way to enhance critical current for the present CT-OP Bi-2223 tape. Our results show the feasibility for 300 A-class I c at 77K. [ABSTRACT FROM AUTHOR]