Growth and dissolution of He-3 liquid drops in a He-4 crystalline matrix

Pressure measurements are used to study the kinetics of phase separation of He-3-He-4 solid solutions under conditions such that after the transition a two-phase system is formed, consisting of liquid drops of the concentrate d phase (nearly pure He-3) in a crystalline matrix of the dilute phase (nea rly pure He-4). It is shown that under stepped cooling of the two-phase sam ple the growth of the liquid drops can be described by a superposition of t wo exponential functions representing processes with long and short time co nstants. This is due to the strong influence of the stresses arising in the crystal at the phase transition owing to the large difference in the molar volumes of the two phases and which probably cause plastic deformation of the matrix and the giving rise to nonequilibrium concentrations of He-3 in it. The transport of He-3 atoms occurs only in connection with stress relax ation. It is established that cyclic processes of growth and dissolution of the liquid drops strongly degrade the quality of the crystal and lead to a n increase of the pressure. The possibility that a mixture of the liquid an d crystal exists in the drops is also analyzed. (C) 2000 American Institute of Physics. [S1063-777X(00)00406-0].