Microstructure and Thermal Conductivity Modeling of Granular Nanoplatelet Assemblies

Consolidation and sintering of bismuth telluride nanoplatelets is a cost-effective method of manufacturing high thermoelectric figure-of-merit materials. A structural optimization method is employed here to study the effects of columnar structures formed by nanoplatelet composites on thermal transport. The initially sparse and random distribution of nanoplatelets is compacted into a jammed state under an external hydrostatic stress, thereby simulating the compaction of nanopowders in experiments. The jammed morphology exhibits randomly oriented stacks of nanoplatelets and a discontinuous distribution of the pore phase within the microstructure. Grain and pore morphologies are statistically quantified using computational geometry techniques. High aspect ratio nanoplatelets exhibit large degree of stacking that results in large pore size heterogeneity. Quasi-ballistic heat conduction through the grain phase is modeled using a Landauer approach. The volume fraction and morphology of the discontinuous pore phase strongly influences thermal conductance by providing sites for phonon scattering at pore–grain interfaces. A thermal model incorporating interface scattering is employed to explore the relationship between microstructure and thermal transport.