Reducing Effective Mass for Advancing Thermoelectrics in Sb/Bi-Doped AgCrSe₂ Compounds
2020
Tang, Mingjing | Chen, Bangxian | Guo, Xuming | Zhang, Fujie | Zhong, Yan | Liu, Hangtian | Kang, Bin | Ang, Ran
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 Ag₀.₉₇CrSe₂, i.e., Ag₀.₉₇Cr₁–ₓ(Sb/Bi)ₓSe₂, 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 Ag₀.₉₇Cr₀.₉₇Sb₀.₀₃Se₂. The current finding provides an excellent avenue for advancing thermoelectrics in AgCrSe₂ materials.
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