Contribution of phonon and vacancion excitations to the thermodynamic properties of solid helium

Precision measurements of the temperature dependence of the pressure are made on high-quality crystals of He 4 and He 3 – He 4 solutions grown at a constant volume. The phonon and vacancion contributions to the pressure are separated on the basis of the Debye model for the phonons and the model of wide-band vacancion excitations. This approach is also used to analyze all the other available thermodynamic data for the solid pure isotopes of helium and their solutions. This yields information about the Debye temperature and vacancy activation energy, and a universal dependence of these parameters on the molar volume is found for He 3 , He 4 , and He 3 – He 4 solutions. The values found for the corresponding Grüneisen parameters turn out to be independent of the molar volume.