Revealing the decisive factors of the lattice thermal conductivity reduction by electron-phonon interactions in half-Heusler semiconductors

The role of electron-phonon (EP) scattering in lattice thermal conductivity (kappa L) of thermoelectric material has not been fully studied until now, especially for the decisive factors that influence the reduction of kappa L. To address this issue, we report the effect of EP interactions on kappa L at a series of temperatures and carrier concentrations for 18 half-Heusler compounds. Among all the compounds investigated, the hole-doped TiCoSb and the electron-doped ZrIrSb have the largest kappa L reductions (32% & 20%) by EP interactions at 300 K, under the carrier concentration of 1021 cm-3. Detailed analyses reveal that the system with strong EP coupling strength and high electronic density of states at the Fermi level (N (EF)) favor the kappa L reduction, because these two factors are beneficial for EP scattering rates. And a high N (EF) can be caused by a high carrier concentration and/or a large effective mass. Temperature is another factor that affects the reduction of kappa L by EP interactions due to its imbalance influence on EP and phonon-phonon (PP) scatterings. Furthermore, after considering the influences from the aliovalent doping and grain boundary, the EP interactions still play a non-negligible role on kappa L reduction, especially at low temperatures and high carrier concentrations. Our work provides a complete picture for understanding the mechanism of EP interactions in material's thermal transport.