Our next Superconductivity Talk is Friday, 24 April 2026.
Superconductivity Talks is a premier virtual platform designed
to highlight the contributions of the next generation of researchers.
Join us on Friday, April 24, 2026, at 11 AM EST / 5 PM Switzerland
Topic: Internal oxidation for the fabrication of multifilamentary Nb3Sn wire with high-Jc
Speaker: Gianmarco Bovone
Speaker Bio:
Gianmarco Bovone obtained his PhD in Materials Science in 2016 from the Università degli Studi di Genova, where his research focused on the introduction of nanoprecipitates in MgB2 superconductors. In 2017, Gianmarco joined the Applied Superconductivity Center (ASC) at the National High Magnetic Field Laboratory (NHMFL) in Tallahassee, where he continued research on MgB2 and expanded his work to iron-based superconductors.
Since 2019, he has been working at the Université de Genève, focusing on the implementation of internal oxidation in industrial Nb3Sn wires to enhance the critical current density, a key objective for the realization of the Future Circular Collider.
Abstract:
To enhance the critical current density (Jc) to meet the requirements of the Future Circular Collider (FCC-hh), we implemented internal oxidation in multifilamentary Rod-In-Tube wires. Internal oxidation involves alloying Nb with highly electropositive elements (Hf or Zr) and introducing an oxygen source (OS), typically SnO2 powder. This process promotes the precipitation of oxide nanoparticles (HfO2 or ZrO2), which act as artificial pinning centers (APCs) and refine the Nb3Sn grain structure, thereby increasing grain boundary density.
For wires reacted at 650 °C for 200 h, the combined presence of Hf and OS reduced the Nb3Sn grain size to below 50 nm and increased the layer Jc to 3700 A/mm2 at 15 T and 4.2 K. In contrast, wires fabricated from the same precursor alloys but without OS exhibited grain sizes exceeding 100 nm and a layer Jc below 2100 A/mm2 under the same conditions.
The APCs enhance flux pinning through a point-defect mechanism, as evidenced by a shift of the pinning force peak to 0.3 of the reduced field (b, defined as the applied field divided by the upper critical field). Transmission electron microscopy (TEM) shows that HfO2 forms smaller APCs than ZrO2 (approximately 4 nm and 15 nm, respectively, after reaction at 650 °C for 200 h). In addition to average particle size, the size distribution of APCs is critical to ensure effective interaction with the flux-line lattice.
Increasing the heat-treatment temperature modifies the APCs size distribution, reducing their pinning efficiency, leading to a decrease in layer Jc. This occurs even though the Nb3Sn grain size remains below 70 nm, highlighting the dominant role of APCs in Jc enhancement.
Overall, these results demonstrate that incorporating an internal oxidation in industrial multifilamentary Nb3Sn wires is essential to achieve significant Jc improvement through a modified pinning mechanism.