High-precision pressure measurements in solid 4 He, grown by the capillary blocking technique, have been made in temperatures range from 50 to 500 mK. The temperature dependence of pressure indicates that aside from the usual phonon contribution ϳT 4 , there is an additional contribution ϳT 2 , the latter becoming dominant at temperatures T Ͻ 300 mK, where an abnormal behavior attributed to supersolidity has been observed. The data suggest the appearance of a glassy phase ͑that might be responsible for the anomalous behaviors observed previously͒. A dramatic pressure decrease has been observed under annealing of the samples. The glassy contribution to the pressure can be eliminated in well-annealed crystals.

A series of experiments has been performed to investigate the conditions of formation of a disordered (glass-like) state in crystals of 3He. With the help of precise measurements of pressure at constant volume it has been established that a glass phase is formed easily in rapidly cooled crystals grown under homogeneous temperature conditions in the presence of large numbers of nucleation centers. This phase can be removed only by careful annealing. This result has been found in both 3He and 4He, and is independent of type of quantum statistics and determined mainly by crystal growth conditions. An analysis of similar measurements has been performed using a different cell where during the crystal growth a directed temperature gradient was created. In this case, additional defects created as a result of deformation of the crystal were necessary to form a glass-like phase. The degree of deformation of a crystal, achievable in the experiment, was sufficient to form a glass-like phase in solid 4He, but not in a crystal of 3He where the atoms have a large amplitude of zero-point oscillations. Analyzing a temperature dependence of pressure, a study of the features of a phonon contribution to the pressure was also carried out. It was found that in both crystals 3He and 4He at different thicknesses of samples the phonon pressure differs by several times. This effect is qualitatively explained by that that in thin samples an interaction among layers of atoms becomes stronger. This leads to decreasing the phonon contribution to the thermodynamic properties of the helium crystal at low temperatures.

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