Phase Boundary Metallization Enables Electron-Phonon Transport Decoupling in PbS-Based Thermoelectric

Lead sulfide (PbS) is a promising mid-temperature thermoelectric material, but its performance is constrained by high lattice thermal conductivity (κ_lat) and relatively low carrier mobility. Traditional construction of nanoscale second phases can effectively suppress κ_lat, but severely impairs carrier mobility. Herein, phase boundary metallization is engineered to simultaneously achieve the electron-phonon transport decoupling in PbS. Specifically, through substantial Cu introduction and Te substitution, the metallic Cu-enriched phase bridges the PbS matrix and the low-miscibility PbTe phase at the grain boundary, thereby forming a metallized Cu semi-coherent interface. Microstructural characterization has further confirmed that massive Cu accumulation at the grain boundaries forms semi-coherent phase interfaces, which serve as fast channels for carrier transport while enhancing phonon scattering at the interfaces. Therefore, this strategy not only increases carrier mobility to ≈1037 cm² V⁻¹ s⁻¹, but also significantly reduces lattice thermal conductivity to ≈0.85 W m⁻¹ K⁻¹ at 300 K in PbS_0.6Te_0.4-1.4%Cu sample. Ultimately, a room-temperature ZT of 0.37 and an average ZT of 0.70 (300–773 K) are achieved, with a measured 5.5% conversion efficiency at ΔT = 408 K. This approach of decoupling electron-phonon transport via phase boundary metallization provides new perspectives for developing high-performance thermoelectrics.