We show here that yttrium is immiscible and precipitates with various sizes in the body centered cubic V0.6Ti0.4 alloy superconductor. The number and size of the precipitates are found to depend on the amount of yttrium added. Precipitates with various sizes up to 30 μm are found in the V0.6Ti0.4 alloy containing 5 at. % yttrium. The large amount of line disorders generated by the addition of yttrium in this alloy is found to be effective in pinning the magnetic flux lines. While the superconducting transition temperature increases with the increasing amount of yttrium in the V0.6Ti0.4 alloy, the critical current density is maximum for the alloy containing 2 at. % yttrium, where it is more than 7.5 times the parent alloy in fields higher than 1 T. We found that the effectiveness of each type of defect in pinning the flux lines is dependent on the temperature and the applied magnetic filed.

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.

The morphological, transport and terahertz optical properties of DC magnetron sputtered granular molybdenum thin-films with nano-grains embedded in an amorphous matrix have been studied in the normal and superconducting states. The superconducting transition temperatures of these films are much higher than that of bulk molybdenum. The optical properties of these thin-films have been studied using terahertz time-domain spectroscopy. Their properties have been compared with the existing materials used for the development of radiation detectors. The resistivity of the films lies in >100 µΩ-cm range which is ideal for making highly sensitive radiation detectors. The Hall measurements indicate the presence of holes as the dominant carriers with very small mean free path and mobility. In the normal state, the films are disordered bad metal but they have large superfluid density and stiffness in their superconducting state. The normal state and superconducting properties of the films are very promising for their use in cryogenic radiation detectors for microwave, terahertz, and far IR frequency ranges.