CHARACTERISTIC BEHAVIOR OF THE SPECIFIC-HEAT OF EXSOLVING HE-3-HE-4 SOLID-SOLUTIONS

A theory that includes a substantial contribution of the correlation e ffects to the specific heat of exsolving He-3-He-4 solid solutions is constructed on a lattice-gas model. This theory makes it possible to c onstruct a unified description of the temperature variation of the spe cific heat of these systems for a wide range of values of the He-4 imp urity density n(0). It is shown that, to obtain quantitative agreement of the proposed theory with published experimental data, the effectiv e coordination number z for the impurity in the solution must be treat ed as an adjustable parameter. For concentrated solutions (5%<n(0)<50% ) the optimal value z similar or equal to 250 is independent of densit y, while for dilute solutions (n(0)<5%) it decreases with n(0). Specif ically, z=5 for n(0)=0.28% and z=3 for n(0)=0.11%. This suggests that a second phase can precipitate in the form. of low-dimensional fractal structures during the exsolution of dilute solutions. (C) 1998 Americ an Institute of Physics.