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The effect of Cr diffusion on the residual resistance ratio (RRR) values of [Nb.sub.3]Sn strands is studied by using the KSTAR and ITER candidate strands. The studies have shown that the RRR variation is mainly affected by the 20 K resistivity or by chrome diffusion and the other characteristics are not degraded but have rather improved.

A study was conducted on the growth conditions of a cylindrically textured YBCO film on a cylindrically curved surface of single crystalline YSZ. Oxygen ion milling and CeO2 buffer layer deposition were used for the pretreatment of the substrate surface. XRD 2 theta-scan and phi-scan revealed that the a- and b-axes were aligned and that the c-axis was normal to the surfaces.

Field, temperature, and strain dependences of the critical current for a SiC doped multifilamentary in situ MgB2 wire have been studied. Measurement results were compared with that of the undoped wire, and the origin of the difference in the critical current is discussed. The critical current can be calculated with the percolation model considering the effect of anisotropy. The temperature dependence of the fitting parameters, the upper critical field along the ab-plane, and c-axis is compared with the dirty-limit two-gap theory. To assess the validity of the fitting parameters, resistive transition has been measured especially to extract the upper critical field directly. It is shown that even the resistive broadening can be well explained by a simple parallel path model using the fitting parameters obtained from the critical current analysis. [ABSTRACT FROM AUTHOR]

Angular dependence of the critical current in a varying Lorentz-force configuration for a SmBCO coated conductor has been studied. Near the transition temperature, the angular dependence of the critical current in a varying Lorentz-force configuration was quite similar to the result of a constant Lorentz-force measurement. As the temperature is lowered and as the field is aligned along the ab-plane, the critical current measured in a varying Lorentz-force configuration becomes larger than the constant Lorentz-force measurement. We found that the field dependence of the critical current and n-value can be described by the same pinning model, the Kramer model including thermal activation, reported for constant Lorentz-force measurements of various ReBCO (Re, rare earth, Sm, or Y) thin films [S. Oh et al., J. Appl. Phys. 102, 043904 (2007)]. As a possible reason, the Lorentz force acting on segments of twisted vortex lines due to collective pinning or by thermal excitations is discussed. It is further argued that the difference in the critical current for the varying and constant Lorentz-force measurements can be understood as mainly due to a variation in the pinning force, if we interpret the Lorentz force on twisted vortex lines as a scalar product between the applied field and current. [ABSTRACT FROM AUTHOR]

A comprehensive study of the effects of carbohydrate doping on the superconductivity of MgB2 has been conducted. In accordance with the dual reaction model, more carbon substitution is achieved at lower sintering temperature. As the sintering temperature is lowered, lattice disorder is increased. Disorder is an important factor determining the transition temperature for the samples studied in this work, as evidenced from the correlations among the lattice strain, the resistivity, and the transition temperature. It is further shown that the increased critical current density in the high field region can be understood by a recently-proposed percolation model [M. Eisterer et al., Phys. Rev. Lett. 90, 247002 (2003)]. For the critical current density analysis, the upper critical field is estimated from a correlation that was reported in a recent review article [M. Eisterer, Supercond. Sci. Technol. 20, R47 (2007)], where a sharp increase in the upper critical field by doping is mainly due to an increase in lattice disorder or impurity scattering. On the other hand, it is shown that the observed reduction in self-field critical current density is related to the reduction in the pinning force density by carbohydrate doping. [ABSTRACT FROM AUTHOR]

Detailed field and angle dependencies of the critical current and the n value for a SmBCO coated conductor have been measured. It was found that the field dependence of the n value can be fitted by an empirical power law with three parameters including the irreversibility field. We also found that there is a correlation between the critical current and the n value which can be described by the Kramer model including thermal activation. The model fits the field dependence of the empirical critical current data at various angles and temperatures with three fitting parameters, the pinning force maximum, the g factor, and the upper critical field. The upper critical field found from fitting was higher than the irreversibility field, and the angular dependence of the upper critical field is in agreement with the Tinkham model. The pinning force maxima do not show a correlation with the upper critical or the irreversibility fields, which is attributed to the difference in the pinning mechanism with a variation of the angle. It was further shown that the angular dependence of the critical current can be calculated by the Kramer model including thermal activation with empirical angular dependence expressions for each parameter. The critical current data reported by Yamada et al. [Supercond. Sci. Technol. 17, S25 (2004)] for YBCO thin films on various substrates deposited by pulsed laser deposition method can also be described by the Kramer model including thermal activation and the angular dependencies of each parameter were compared with the SmBCO coated conductor fitting results. [ABSTRACT FROM AUTHOR]

The transition temperature T(sub c), the thermodynamic critical field B(sub c), and the upper critical fields B(sub c2) of Nb(sub 3)Sn were numerically calculated by Eliashberg theory of strongly coupled superconductors using the Einstein spectrum. It was found that the impurity concentration was relatively low and the strain effects were due to the phonon mode softening both at high and low frequencies.