Realizing High Thermoelectric Performance in GeTe-Based Supersaturated Solid Solutions

As a highly promising thermoelectric material in the mid-temperature region, pristine GeTe shows deteriorated thermoelectric properties due to the low Seebeck coefficient and the intrinsic high thermal conductivity. Herein, it is discovered that the introduction of strongly correlated d, f electrons by alloying rare-earth atoms at Ge sites will increase the band effective mass and promote band convergency, which can largely improve the electric transport property. Moreover, the heavy atoms (Pb, Bi) doping induces optical phonon softening and the avoided crossing between acoustic and optical phonon branches, decelerating both optical and acoustic phonon velocities. The modulated composition wave from the fluctuated multi-component distribution introduces a complicated hierarchical structure including point defects and nanoprecipitates, which provides all-scale scattering sources for heat-carrying phonons and results in low lattice thermal conductivity. Consequently, a high zT of 2.4 at 800 K can be obtained in the Ge0.86Pb0.09Bi0.03Ce0.005Te sample due to the combination of strong correlation for d, f electrons and the full-spectrum scattering for phonons. This work provides an effective strategy to increase the thermoelectric performance of IV-VI compounds by combining the modulated band structure and the softening phonon dispersion. The low Seebeck coefficient and the high thermal conductivity deteriorate the thermoelectric properties of GeTe. Herein, the Seebeck coefficient is enhanced by promoting band convergency induced by the strongly correlated d, f electrons of rare earth elements. The doping of Pb and Bi causes avoided crossing and hierarchical structure, strengthening the full-spectrum scattering of phonons and decelerating the sound velocity. image