Enhanced critical current density in the low-temperature sintered Nb3Al superconductor with Sn doping

The Nb3(Al1-xSnx) superconductors (x = 0.05, 0.15, 0.25, 0.35) were prepared by mechanical alloying and subsequent low-temperature sintering. It was found that the critical current density (Jc) of the obtained Nb3(Al1-xSnx) sample is enhanced significantly compared to undoped Nb3Al prepared using the same method. The maximum value of the Jc reaches up to 5.10 × 104 A·cm−2 (4.2 K, 5 T) for Nb3(Al0.85Sn0.15) sample. Combined with the phase composition analysis and microstructure observation, it is indicated that Sn enters the A15 crystal structure of Nb3Al forming the Nb3(Al1-xSnx) phase after low-temperature sintering. What's more, Sn doping improves the grain connectivity as well as refines the grain size of Nb3Al, which are the main reasons for the enhancement of Jc in the Sn doped samples. Based on the exploration of the phase evolution of Nb–Al–Sn system during the mechanical alloying and subsequent low-temperature sintering process, it is also confirmed that Nb3Sn forms firstly during the sintering process and then can serve as the perfect nucleus of Nb3Al to increase its nucleation rate, leading to the significant decrease of the grain size of Nb3Al.