Critical current and microstructure of diffusion Nb3(Al,Ge) alloys

Pinning centres are studied in composite bands on the base of the superconductive copper-alloyed Nb3(Al, Ge) compound. Electron-microscopic studies in alloyed and nonalloyed bands allowed revealing the reason of the critical current Isub(c) increase in bands with copper after low-temperature annealing (LTA). Measurements in the band critical current right after high-temperature heating and after LTA made it possible to determine a relative contribution of pinning centres of different kinds: grain boundaries of the compound and the second phase particle precipitation. The effect of LTA on the band microstructure and superconductiVe properties is studied. It is stated that the critical current density after LTA at 800 deg C does not practically depend on the layer thickness in the Nb3(Al, Ge) compound and is equal to approximately 2x105 A/cm2 in a 55 kOe magnetic field