Robust high-field superconductivity in Sc- and Al-substituted Ti0.5(ZrNbTaHf)0.5 high-entropy alloys

High-entropy alloy superconductors provide a useful platform for studying superconductivity in strongly disordered metallic systems. Here, we investigate the effect of chemically distinct substitutions on the high-field superconducting state of the Ti-rich high-entropy alloy Ti0.5(ZrNbTaHf)0.5. Polycrystalline samples of Ti0.475(ZrNbTaHf)0.475X0.05, where X = Al, Sc, were synthesized and characterized by x-ray diffraction, electron microscopy, magnetic susceptibility, electrical resistivity, and specific heat measurements. Both substitutions preserve the average bcc structure, although local compositional modulations, mainly associated with Ta-rich regions, remain present. Magnetic and thermodynamic measurements show superconducting transitions near 5.2 K in both alloys, indicating a reduction of critical temperature relative to the parent compound. In contrast, the upper critical field is largely unaffected: analysis of the specific-heat-derived upper critical field μ0Hc2(T) curves using the Werthamer–Helfand–Hohenberg model yields μ0Hc2(0) = 13.2(1) T for the Al-substituted alloy and 13.3(1) T for the Sc-substituted alloy. These values exceed the weak-coupling Pauli limit and remain close to that of the parent alloy. The results indicate that high-field superconductivity in this Ti-rich high-entropy alloy is robust against chemically distinct low-level substitutions, even when Tc is suppressed.