Superconducting Properties of Nb3Sn Superconductors, Doped With Ti, Zr and Ti, Ti and Ta

The paper presents the results of a study of three types of internal tin Nb3Sn strands of the same design, differed by the way of doping with titanium, titanium and zirconium, titanium and tantalum. The diameter of the fabricated strands was 1.0 mm. For the formation of the superconducting phase, a series of two steps heat treatments (HT) were carried out. The temperature of the reaction second stage of HT was varied from 665 to 720 °C. The microstructure of the Nb
₃
Sn layer after HT was studied by scanning electron microscopy. Transport properties of the strands samples were measured in magnetic fields up to 24 T. The interrelation of the HT regimes and superconducting properties of the strands investigated, including RRR, Tc and Jc has been analyzed. It has been shown that with an increase of the temperature of the second stage of heat treatment the critical temperature of samples doped with two elements tends to increase more rapidly compared to a sample doped only with titanium. Studies of the critical current density of the samples in the wide magnetic field range as a function of the HT second stage temperature are presented.