Effect of dopant solubility and excess doping on the superconducting properties of doped Nb3Sn prepared by field assisted sintering technique

The present work is focused on understanding the role of Ruthenium (Ru) and Yttrium (Y) on the superconducting properties of the A15 Nb₃Sn intermetallic compound. Ru and Y shows different solubility limit within the Nb₃Sn matrix. Ru and Y-doped Nb₃Sn superconducting alloys were prepared through mechanical alloying (MA) route followed by sintering using Field Assisted Sintering Technique (FAST). Analysis by X-ray diffraction demonstrates a significant decrement in crystallite size up to 0.5 wt% for the Ru-doped Nb₃Sn followed by a significant increment when doping level reaches 1 wt% Ru. This could be the combined effect of structural disorderliness and Ru dissolution within the Nb₃Sn matrix. While a significant increase in the crystallite size is observed for 0.5 wt% Y-doped Nb₃Sn and no further change up to 1 wt% Y. This change could be a result of limited solubility of Y within the Nb₃Sn matrix. Meanwhile, excessive Y plays an important role in the formation of additional flux pinning centers. The critical current density (J_c) shows a significant increase for all the Y-doped Nb₃Sn alloys by a factor of 29 % due to the formation of Y₂O₃ from the residual Y, which is assumed to serve as additional flux pinning center. The Y₂O₃ particles was also considered as a possible cause of pinning down of grain boundaries in addition to NbO leading to grain refinement through Zener pinning. Ru-doped Nb₃Sn alloys also exhibit an increase in J_c compared to pristine Nb₃Sn, but only in concentrations up to 0.5 wt% Ru. At higher applied field, even 1 wt% Ru shows slight increase in J_c than pristine Nb₃Sn. Y-doped samples showed superior functional properties.