Features of the temperature dependence of the pressure of solid helium at low temperatures

A series of experiments have been performed to find out the conditions for formation of disordered (glassy) state in ^3He crystals. The high-precision pressure measurements at constant volume demonstrated that a glassy phase was easily generated in quenched cooled crystals grown under uniform temperature conditions in the presence of big number of nuclei and could be removed only after careful annealing. This result was found in both ^3He and 4He. It does not depend on the type of quantum statistics and is defined mainly by the conditions of the crystal growth. Analysis of similar measurements also was made for some other cell, where the temperature gradient was created in the process of crystal growth. In that case an additional number of defects, created due to deformation of the crystal, were required for formation of a glassy phase. The degree of crystal deformation achieved in the experiment was sufficient for the formation of glassy phase in solid 4He, but not in 3He, where the atoms had higher amplitude of zero-point oscillations. The temperature dependence of pressure was used to study the features of phonon contribution to pressure. It is found that in crystals of both ^3He and 4He, the phonon pressure differs by several times at different thicknesses of the sample. The qualitative explanation of this effect implies that in thin samples interaction between atomic layers becomes stronger, resulting in decreasing the phonon contribution to the thermodynamic properties of the crystal at low temperature. PACS: 67.80.-s Quantum solids.