Rubets S. Homogenization and phase separation of concentrated solid 3Не–4Не solutions

The dissertation presents the results of search and investigation of new effects arising during the two first kind phase transitions– the phase separation of concentrated solid 3He–4He solutions and the reverse transition of the separated solution into a homogeneous state. Anomalous behavior of the solution pressure near the phase transition was observed. When the solution is cooled, its pressure does not decrease owing to decreasing in the phonon contribution, but increases noticeably. It was established that at approaching the phase separation temperature the nuclei of new phase are formed like a clusters containing hundreds of atoms due to fluctuations in the solution impurity subsystem. It is shown that the rate of the initial homogenization stage can exceed the velocity of the separation more than 500 times. In this case, new feature has been discovered: the homogenization rate essentially depends on the kinetics of the preceding separation. The results of experiments on the separation kinetics of concentrated 3He–4He solutions and their analysis within the framework of the new–phase growth theory with the corresponding diffusion processes made it possible to find the mass diffusion coefficient and construct the general picture of the evolution of diffusion processes with increasing concentration. In concentrated solutions, the localization of impurity excitations at sufficiently high concentrations leads to a sharp drop in the mass diffusion coefficient. In spite of this, the phase separation process goes quite intensively, since with the increase in concentration the number of nucleation centers increases, that is, the diffusion length of impurity atoms decreases.