High Critical Temperature and Field Superconductivity in Nb$_{0.85}$X$_{0.15}$, (X = Ti, Zr, Hf) Alloys: Promising Candidates for Superconducting Devices
Niobium and its alloys with early transition metals have been extensively studied for their excellent superconducting properties. They have high transition temperatures, strong upper critical fields, and high critical current densities, making them ideal for superconducting applications such as SQUIDs, MRI, NMR, particle accelerators, and Qubits. Here we report a systematic investigation of as-cast Nb-rich alloys, Nb$_{0.85}$X$_{0.15}$ (X = Ti, Zr, Hf), using magnetization, electrical transport, and specific heat measurements. They exhibit strong type-II bulk superconductivity with moderate superconducting transition temperatures and upper critical fields. The estimated magnetic field-dependent critical current density lies in the range of 10$^5$--10$^6$~A/cm$^2$ across various temperatures, while the corresponding flux-pinning force density is on the order of GNm$^{-3}$, suggesting the potential of these materials for practical applications. Electronic-specific heat data reveal a strongly coupled, single, isotropic, nodeless superconducting gap. These Nb-rich alloys, characterized by robust superconducting properties, hold significant potential for applications in superconducting device technologies.