Predicting thermoelectric figure of merit in complex materials: What do we need to know?

In a complex nanostructured material or composite, the thermoelectric figure of merit, Z T ( T ) , is strongly dependent on the morphology and transport properties of interfacial areas that connect individual crystal grains or composite constituent phases. Despite the active efforts to improve Z T ( T ) , relatively few experimental and theoretical investigations have been focused on probing the interfacial transport properties of relevant materials. We developed a finite element method based mesoscale-level simulation approach to evaluate the effective values of thermal and electrical conductivities, and Seebeck coefficient in structurally complex materials. This approach was tested on three popular nanocrystalline thermoelectric systems: n-type Si, n-type Si _0.80Ge _0.20, and p-type BiSbTe, providing excellent agreement between the simulated and previously measured values of Z T ( T ) . The interfacial thermoelectric properties of these material systems were quantified in the process and compared to simple models. Furthermore, the sensitivity of Z T ( T ) to changes in the system morphology was elucidated as well.