The thermal conductivity component associated with lattice vibrations is one of the quantities determining the thermoelectric activity of a material. We have simulated the dependences of phase composition and the phonon component of the thermal conductivity associated with it on the shape of nanoparticles of a Bi–Sb alloy with an equiatomic composition and with core–shell configuration. The shape of a particle is simulated by a coefficient corresponding to the extent of deviation of the particle shape from spherical or by its fractal dimension. It is shown that mutual solubilities of components depend on the nanoparticle shape and on the mutual arrangement of coexisting phases, and the thermodynamic equilibrium position for particles with complex morphology corresponds to the homogeneous state. Homogenization of a nanoparticle reduces the phonon component of its thermal conductivity by 70–80%.
In this paper, thermodynamical approach has been used to simulate the influence of shape on phase equilibria in the two-phase-region between liquidus and solidus temperatures in case of Si-Ge alloy nanoparticles. Volumes and shapes of considered nanoparticles have been described by their effective radii and fractal dimensions, the dependence of fractal dimensions on temperature has been obtained using a simple geometrical model. It has been shown that decreasing the volume of a nanoparticle and its fractal dimension (which corresponds to nanoparticles of a more complicated shape) leads to narrowing down the temperature range of the heterogeneous region and changes the phase transition temperatures and equilibrium compositions of co-existing phases. At different temperatures, the dependences of the composition of the liquid phase differ which is explained by implementing different mechanisms of reducing the surface energy.
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