X-Ray Absorption Spectroscopy to investigate precipitated oxides in Nb3Sn wires with an internal oxygen source

Internal oxidation can achieve significantly enhanced J_c in Nb ₃ Sn wires, but the mechanism of oxygen transport and oxide precipitation is not fully understood. Our investigation employs X-ray Absorption Near-Edge Structure (XANES) spectroscopy, revealing insights into the oxidation of Zr and its interaction with oxygen in different areas of the wire cross section. We discovered that in samples reacted at 650°C the majority of Zr in the Nb ₃ Sn layer is oxidized as ZrO ₂ , whereas it predominantly remains non-oxidized within the residual alloy. This is an interesting finding especially for samples where oxygen has to diffuse first through the entire layer of Nb alloy to reach the regions where Nb ₃ Sn will form. The onset critical temperature ( T_c ) of the residual Nb alloy was the lowest in such samples, most probably due to a higher content of interstitial oxygen resulting from the diffusion gradient. This report adds to existing indications that ZrO ₂ precipitates in superconductors employing internal oxidation are only located within the Nb ₃ Sn layer and opens new avenues of research on the formation of this precipitates.