In developing superior thermoelectric conversion devices, it is key to reduce the thermal conductivity of the materials. Since heat is carried by lattice vibrations (phonons) in most solids, enhancing the phonon scattering via the nanocrystallization of materials is considered effective for the reduction of their thermal conductivity. To this effect, numerical studies have attempted to elucidate the relationships between thermal conductivity and polycrystalline nanostructure characteristics. However, the previous analyses have been applied only to idealized polyhedral aggregates created by purely mathematical means such as the Voronoi tessellation; a method to evaluate heat transfer characteristics using more realistic grain structures has yet to be established. In this study, we combine the phase-field and phonon transport simulations to establish a numerical framework that can perform thermal conductivity evaluations for physically-based polycrystalline nanostructures. In this method, polycrystalline nanostructure formations are first simulated using a multi-phase field model, which is an extension of the phase-field method to multi-phase/polycrystalline systems. Mesh data of the grain boundary faces are then generated from the simulated polycrystalline structures and used for thermal conductivity evaluations based on phonon transport analysis. In the presentation, we apply the developed method to grain growth phenomena in nano-polycrystalline inorganics, revealing how the nanostructural evolutions through grain growth affect thermal conductivity.

In this study, we combine the phase-field and phonon transport simulations to establish a numerical framework that can perform thermal conductivity evaluations for physically-based polycrystalline nanostructures. In this method, polycrystalline nanostructure formations are first simulated using a multi-phase field model, which is an extension of the phase-field method to multi-phase/polycrystalline systems. Mesh data of the grain boundary faces are then generated from the simulated polycrystalline structures and used for thermal conductivity evaluations based on phonon transport analysis. In the presentation, we apply the developed method to grain growth phenomena in nano-polycrystalline inorganics, revealing how the nanostructural evolutions through grain growth affect thermal conductivity.