Analysis of the Lattice Specific Heat of Mo:Re Alloy

The low-temperature lattice specific heat of a Mo- 5-at.%-Re alloy has been successfully explained on the basis of a Green's-function theory. We take into account the effects due to change in mass at the substitutional impurity site and also the changes in the nearest-neighbor central and noncentral force constants for the impurity-host-crystal interaction. The enhanced specific heat is dominated by force-constant changes and very much sensitive to these changes. It is observed that the contribution of the even parity $A_{1g}$, $E_g$, $F_{1g}$, and $F_{2g}$ modes are very significant and, in fact, dominate over that of $F_{1u}$ symmetry modes in the low-temperature side of the specific-heat curve. However, at higher temperatures more resonance modes appearing in $F_{1u}$ irreducible representation are excited and their contribution dominates over all others. The present values of the defect parameters are found to be quite similar to those obtained earlier by elastic-constant data.