Modeling Grain Boundary Scattering in Nanocomposites

Modeling the thermoelectric properties of nanocomposites is difficult due to the complex grain boundary scattering processes which scatter both electrons and phonons. In this work we introduce several models which characterize the grain boundary scattering rate. This scattering rate is incorporated into a code we developed which numerically calculates the electrical and thermal properties of bulk and nanocomposite thermoelectric materials using the Boltzmann equation under the relaxation time approximation. The code is capable of calculating all the relevant thermoelectric properties over a wide range of temperatures, doping concentrations, and compositions, allowing for a full characterization of the material. We formulate two grain boundary scattering rates and implement the commonly used Mayadas model. The code and all of the grain boundary scattering models are then validated on bulk data for SiGe and applied to nano-SiGe. All the models are able to fit the experimental data after a fitting parameter is suitably chosen, so we determine which model is most appropriate based on the physical assumptions made by each model.