The V-Ti alloys are promising materials as alternate to the commercial Nb-based superconductors for high currenthigh magnetic field applications. However, the critical current density (Jc) of these alloys are somewhat low due to their low grainboundary density. We show here that grain refinement of the V-Ti alloys and enhancement of the Jc can be achieved by the addition of Gd into the system, which precipitates as clusters along the grain boundaries. Both the Jc and the pinning force density ( ) increase with the increasing Gd content up to 1 At. % Gd, where they are more than 20 times higher than those of the parent V0.60Ti0.40 alloy. Introduction of Gd into the system also leads to ferromagnetic (FM) correlations, and the alloys containing more than 0.5 At. % Gd exhibit spontaneous magnetization. In spite of the FM correlations, the superconducting transition temperature increases slightly with Gd-addition.
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We report here the temperature dependence of electrical resistivity (ρ(T)), heat capacity (C(T)) and thermal conductivity (κ(T)) of superconducting V 1−x Ti x alloys in the absence and presence of external applied magnetic fields. The ρ(T) changes from positive temperature coefficient of resistivity (TCR) to negative TCR at about x = 0.7 indicating that many of these alloys lie close to the Mott-Ioffe-Regel (MIR) limit. The jump in the C(T) across the superconducting transition temperature (T C ) indicates that these alloys are in the intermediate coupling limit. The κ(T) increases in certain V 1−x Ti x alloys as the temperature decreases below the T C indicating that the phonons dominate the heat conduction in the superconducting state, whereas we found that the electrons are the major carriers of heat in the normal state. Our analysis suggests that the unusual features of thermal conductivity have origin in (i) the electron mean free path approaching the inter atomic distances (MIR limit) and (ii) the renormalization of the phonon mean free path due to the presence of point defects and the electron-phonon interaction.
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