Using Bulk Thermoelectric Measurements to Identify Grain Boundary Transitions in NbFeSb

Grain boundaries have seen much recent interest for improving the performance of thermoelectrics, with their capacity to reduce thermal conductivity. Thermally activated charge carrier scattering from grain boundaries is detrimental to performance, far outweighing the benefits to thermal conductivity in many materials. If charge scattering of grain boundaries could be reduced or eliminated, then reducing grain size could be used to improve the thermal properties of many thermoelectrics. In half-Heusler materials, experimental observations have shown that compositional changes at the grain boundary from dopant segregation are correlated to a reduction in the detrimental scattering from boundaries. However, there is currently no good method to identify this behavior based on bulk thermoelectric measurements. In this presentation, we propose a method to model the behavior of grain boundaries such that transitions in grain boundary properties can be identified. This enables the identification of changes in chemistry or structure of grain boundaries prior to in depth characterization of individual grain boundaries in the material.