Analysis of Alkali-Metal Specific-Heat Data

Published data on the density, thermal-expansion coefficient, and compressibility of the alkali metals are reviewed, and best values for the density as a function of temperature and for the Grüneisen constant $\gamma \mathrm{}\left(0\right)\mathrm{}$ are selected. From published specific-heat data the entropy and its corresponding Debye temperature (${\Theta }^S$) are computed as a function of temperature for the body-centered-cubic phase. The values of the first few even moments and some negative moments of the lattice-vibration spectrum are calculated for each alkali metal (bcc phase) on the basis of two different approximations as to the form of the anharmonic specific-heat contribution. The anharmonic contribution is found to be positive for all the alkali metals. There appears to be a systematic change in the shape of the vibration spectrum on going from sodium to cesium. The spectrum moments found for sodium are in good agreement with those obtained from neutron-scattering experiments on this metal.