Exceptionally High <i>H</i> _c${}_{\text{2}}$ Values in Alloyed Bulk Samples of Nb${}_{\text{3}}$Sn

Nb<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${}_{\text{3}}$</tex-math></inline-formula>Sn is the original high-field superconductor but understanding its optimization in wire forms, which are always inhomogeneous, is compromised by a lack of basic understanding of its true property variations when it is alloyed with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub><inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${}_{\text{2}}$</tex-math></inline-formula> enhancing additions (e.g., Hf, Ta, Ti, Zr). Since improving the high-field performance of Nb<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${}_{\text{3}}$</tex-math></inline-formula>Sn is important for many future applications in high energy physics, fusion, and medicine, we are studyingbulk binary and alloyed samples fabricated by ball milling itsconstituent powders and reacting them in a Hot Isostatic Press at pressures up to 2000 bar and temperatures up to 1800 °C. Remarkably, we found that these bulk samples, reacted to produce the A15 phase at temperatures between 1200 and 1800 °C, show minority traces of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub><inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${}_{\text{2}}$</tex-math></inline-formula> (0 K), evaluated with a 99% criterion, that reach almost 40 T, more than 27% higher than the best value previously reported for Nb<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${}_{\text{3}}$</tex-math></inline-formula>Sn. These results are both scientifically interesting but potentially of great practical importance if they can be exploited for improving the high-field properties of Nb<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${}_{\text{3}}$</tex-math></inline-formula>Sn wires. One caution is that these samples do not have added Cu as wires do and that the high <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H_c</i><inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${}_{{2}}$</tex-math></inline-formula> reactions were all done at well above 1000 °C.