Phase separation and diffusion processes in concentrated solid ³He-⁴He mixtures

High-precision pressure measurements of phase separation kinetics were carried out on quantum crystals of concentrated 3He-⁴He mixtures. The 3He with 34.0%, 61.3% and 89.9% content of 3He. The pressure was measured under step-like cooling and heating of the samples. The experimental dependence P(T) observed was compared with the theory based on the diffusion description of kinetic phase separation. That made it possible, for the first time, to obtain information on mass diffusion in the whole concentration range. It is shown that the coefficient of mass diffusion in concentrated mixtures is several orders of magnitude less than that in dilute ones, as a result of interaction between impurities and elastic tension in crystal. At the same time, the phase transition occurs for a relatively short time, because of a high nucleus concentration of a new phase and a small diffusion length.