Superior multiphase interfaces in AgCuTe-based composite with significantly enhanced thermoelectric properties

It is common sense that a phase interface (or grain boundary) could be used to scatter phonons in thermoelectric (TE) materials, resulting in low thermal conductivity (κ). However, a large number of impurity phases are always so harmful to the transport of carriers that poor TE performance is obtained. Here, we demonstrate that numerous superior multiphase (AgCuTe, Ag₂Te, copper telluride (Cu₂Te and Cu_2−xTe), and nickel telluride (NiTe)) interfaces with simultaneous strong phonon scattering and weak electron scattering could be realized in AgCuTe-based TE materials. Owing to the similar chemical bonds in these phases, the depletion region at phase interfaces, which acts as carrier scattering centers, could be ignored. Therefore, the power factor (PF) is obviously enhanced from ~609 to ~832 μW·m⁻¹·K⁻², and κ is simultaneously decreased from ~0.52 to ~0.43 W·m⁻¹·K⁻¹ at 636 K. Finally, a peak figure of merit (zT) of ~1.23 at 636 K and an average zT (zT_avg) of ~1.12 in the temperature range of 523–623 K are achieved, which are one of the best values among the AgCuTe-based TE materials. This study could provide new guidance to enhance the performance by designing superior multiphase interfaces in the TE materials.