  High upper-critical field superconducting alloys are required for
superconducting device applications. In this study, we extensively
characterized the structure and superconducting properties of alloys Ta$_{x}$
Hf$_{1-x}$ (x = 0.2, 0.4, 0.5, 0.6 and 0.8). The substitution of Hf (T$_{C}$ =
0.12 K, type-I superconductor) with Ta (T$_{C}$ = 4.4 K, type-I superconductor)
shows an anomalous enhancement of T$_{C}$ with variation of composition.
Interestingly, all compositions exhibited strongly coupled bulk type-II
superconductivity with a high upper critical field. In particular, for
compositions x = 0.2, and 0.4, the upper critical field (H$_{C2}$) approached
the Pauli limiting field.
