Enhancement of the Lattice Heat Capacity Due to Low-Frequency Resonance Modes in Dilute Aluminum-Silver Alloys

The lattice component of the specific heat of high-purity aluminum and of two aluminum alloys containing 0.5 and 0.95 at.% Ag, respectively, has been measured between 1.3 and 25°K. In the aluminum alloys, an enhancement of the lattice specific has heat been observed which can be explained in terms of low-frequency resonance modes associated with the heavy silver ions. A lattice-dynamical treatment of the heavy-mass defect in a light-host lattice is presented. The calculation is based on the aluminum density of states as obtained from neutron-scattering data, and the silver impurities are treated as mass defects only. The mass-defect calculation accounts for about 80% of the observed specific-heat enhancement. The values of the electronic specific-heat coefficient ${\gamma }_0$ and the Debye temperature ${\Theta }_D$ for pure aluminum are in agreement with previous data.