Anharmonic and Defect Contributions to the Entropy of Solid Argon

The temperature dependence at constant volume of the experimental Debye temperatures for the entropy and the heat capacity at constant volume of solid argon is analyzed taking into account anharmonic effects. The analysis yields values for the geometric-mean frequency and the first few even moments of the harmonic vibrational spectrum, and for the leading anharmonic coefficient in the free energy at high temperature, which provide a test of model calculations of the thermodynamic functions. The excess entropy observed near the melting point is associated with the thermal generation of lattice vacancies, and values for the energy and the entropy of formation of a vacancy in solid argon are obtained therefrom.