Phonon Entropy of Alloying in Dilute Vanadium Alloys

We investigate the entropic effects associated with changes in the phonon modes of vanadium upon dilute substitutional alloying. Using inelastic neutron scattering, we have measured the phonon DOS and the phonon entropy of mixing in V - 6\%X, with X a transition metal impurity. We study trends for impurities across the d-series and down several columns of the periodic table. We show that for Ni, Pd and Pt impurities, the phonon entropy of alloying is large and negative, and in the case of Pt it results in a negative total entropy of mixing for 6\% impurities. A Born-von Karman model was used to invert the experimental DOS curves and showed that the phonon stiffening down this column is associated with an increases in 1NN longitudinal inter-atomic force-constants. The changes in the phonon DOS for impurities across the 3d series are also correlated with the previously measured changes in the superconducting temperature $T_{c}$. Ab-initio DFT simulations were used to compute the effect of impurities on the electronic and phonon properties of vanadium, and are compared to the experimental results. This work was supported by DOE through the BES Grant DE-FG03-0346055 and BES-MS, W-31-109-ENG-38.