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Here we show that addition of Hf to Nb4Ta can significantly improve the highfield performance of Nb$_{3}$Sn, making it suitable for dipole magnets forFuture Circular Collider (FCC). A big challenge for the FCC is that a realisticproduction target for FCC Nb3Sn requires ~30% improvement over currentconductor performance. Recent success with internal oxidation(IO) of Nb-Zrprecursor has shown significant improvement in the layer J$_{c}$ of Nb$_{3}$Snwires, albeit the complication of providing an internal O$_{2}$ diffusion pathand avoiding degradation of irreversibility field($_{irr}$). We compare Zr andHf additions to the standard Nb4Ta alloy of maximum H$_{c2}$ and H$_{irr}$.Nb4Ta rods with 1Zr or 1Hf were made into monofilament wires with and withoutSnO$_{2}$ and their properties measured over the entire superconducting rangeup to 31 T. We found that group IV alloying of Nb4Ta raises H$_{irr}$, thoughadding O$_{2}$ still degrades this slightly. As noted in Nb1Zr studies, thepinning force density F$_{p}$ is strongly enhanced and its peak value shiftedto higher field by IO. A surprising result of this work is that we found betterproperties in Nb4Ta1Hf without SnO$_{2}$, F$_{pmax}$ achieving 2.35 times thatof the standard Nb4Ta alloy, while the oxidized Nb4Ta1Zr alloy achieved 1.54times that of the Nb4Ta alloy. The highest layer J$_{c}$ (16 T, 4.2 K) of 3700A/mm$^{2}$ was found in the SnO$_{2}$-free wire made with Nb4Ta1Hf alloy. Usinga standard A15 cross-section fraction of 60% for modern PIT and RRP wires, weestimated that a non-Cu J$_{c}$ of 2200 A/mm$^{2}$ is obtainable in modernconductors, well above the 1500A/mm$^{2}$ FCC specification. Moreover, the bestproperties were obtained without SnO$_{2}$, the Nb4Ta1Hf alloy appears to opena straightforward route to enhanced properties in Nb$_{3}$Sn wires.

Beneficial influence of Hf and Zr additions to Nb4at.%Ta on the vortex pinning of Nb$_{3}$Sn with and without an O source