Reducing Effective Mass for Advancing Thermoelectrics in Sb/Bi-Doped AgCrSe₂ Compounds

Liquid-like materials have attracted increasing attention, owing to their phonon-liquid electron-crystal feature. As a typical representative, the superionic conductor AgCrSe₂ is regarded as a promising thermoelectric for its intrinsic ultralow lattice thermal conductivity. The primary challenge for achieving high thermoelectric performance is to enhance the inferior electronic performance in AgCrSe₂ compounds. Thus, it is very significant to manipulate band effective mass to achieve a higher power factor. In this work, the Sb/Bi elements are doped at Cr sites in Ag_0.97CrSe₂, i.e., Ag_0.97Cr_1-(Sb/Bi)Se₂, aiming at producing a better overlap of electron orbits between different atoms for sharpening the valence band and decreasing the effective mass. In comparison to pristine AgCrSe₂, a considerable improvement (>50%) in the power factor (∼387 μW m^-1 K^-2 at 750 K) is realized upon 3% Sb doping. The single parabolic band model clarifies that the decreased effective mass and optimized carrier concentration contribute to the enhanced electronic property. Furthermore, an ultralow lattice thermal conductivity (∼0.2 W m^-1 K^-1) is well-maintained for the sample with 3% Sb doping as a result of the nearly unchanged superionic conduction. Eventually, a high peak figure of merit zT (∼0.7 at 750 K) is obtained in Ag_0.97Cr_0.97Sb_0.03Se₂. The current finding provides an excellent avenue for advancing thermoelectrics in AgCrSe₂ materials.