Influence of Ga Addition on Superconducting Properties of <I>in situ</I> Cu-20 mass%Nb-Sn Composites

Overall Jc of in situ Cu-20 mass%Nb-Sn superconducting composites containing 2 and 4 mass% of Ga addition was studied with respect to the dependencies of Sn concentration, heat treatment condition and Ga addition. Microstructures were observed by SEM and EPMA, and the lattice constants of the Cu matrix and Nb3Sn were measured by an X-ray method.The highest overall Jc of 9×108 A/m2 at 9 T and 4.2 K was obtained after heat treatment at 823 K, which was higher than that of the in situ Cu-22.5 mass%Nb-Sn composites without Ga. Furthermore, the Ga addition increases Tc about 0.3 K after heat treatment at 923 K and lowers the heat treatment temperature for obtaining the high overall Jc. It is considered that the improvement of Jc by the Ga addition is caused by the enhancement in Tc and by the grain refinement of Nb3Sn due to the lower heat treatment temperature.