Thermodynamic properties and superconducting transition temperature of vanadium doped with heavy impurities

The low-temperature phonon specific heat of vanadium-based alloys V--Hf, V--Ta, and V--W has been studied theoretically on the basis of a Green's-function technique. A nearest-neighbor impurity model with radial and angular force-constant changes has been employed. The force-constant changes have been evaluated by fitting the measured lattice specific heat of these systems. The effect of volume change has been taken into account. The theory has been modified for comparatively higher concentrations of impurities. The resonances have been found in F sub 1u -irreducible representations only. The local strength constants were found to be quite important in determining the increase or decrease of the transition temperature T sub c . It has been observed that T sub c increases slightly if the force constants for a heavy impurity (Hf) change weakly, and T sub c shifts to lower temperatures (V--Ta, tungsten) if the changes are strong. The electron--phonon and electron--impurity interactions are discussed in detail. The calculated results for both properties are in good agreement with the experimental measurements. 58 ref.--AA