STUDY OF PHASE-SEPARATION KINETICS OF HE-3-HE-4 SOLID MIXTURES BY PRECISION PRESSURE MEASUREMENTS

The kinetics of isotopic phase separation of He-3-He-4 solid mixtures for various molar volumes has been studied by precision pressure measu rements at a constant volume. It is found that the attainment of equil ibrium between coexisting phases formed as a result of stratification is described correctly by an exponential dependence for various modes of crystal cooling and heating. The characteristic phase separation ti me decreases with temperature, thus confirming the athermal quantum na ture of the growth of a new phase during the phase transition. The pha se separation time is found to increase considerably with crystal pres sure. It is shown that the prevailing theory can provide only a qualit ative description of the established regularities. A quantitative desc ription of experimentally observed decay times requires an analysis of diffusion processes in a gas of impurity excitations in the presence of a concentration gradient. (C) 1998 American Institute of Physics. [ S1063-777X(98)00109-1].