Characteristic behavior of the specific heat of exsolving 3He-4He solid solutions

A theory that includes a substantial contribution of the correlation effects to the specific heat of exsolving 3He-4He solid solutions is constructed on a lattice-gas model. This theory makes it possible to construct a unified description of the temperature variation of the specific heat of these systems for a wide range of values of the 4He impurity density n 0. It is shown that, to obtain quantitative agreement of the proposed theory with published experimental data, the effective coordination number z for the impurity in the solution must be treated as an adjustable parameter. For concentrated solutions (5%<n 0<50%) the optimal value z⋍250 is independent of density, while for dilute solutions (n 0<5%) it decreases with n 0. Specifically, 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.

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