Manipulating Pb vacancies achieved ultra-high thermoelectrics in quaternary Pb${}_{0.95}$Na${}_{0.04}$Te${}_{1-x}$Se${}_x$ via fine-tuning Se solubility

Optimizing carrier concentration in PbTe materials can be achieved effectively through the chemical doping of sodium. Nevertheless, the valence balance can lead to the presence of "deleterious defects" in the PbTe matrix, resulting in low sodium solubility at room temperature. Herein, a strategy for fine-tuning Pb vacancies to improve sodium solubility is developed. By a trace amount of Se-doping, the solubility of Na in Pb${}_{0.99}$Te${}_{1-x}$Se${}_x$ through the preservation of Pb vacancies in the matrix is substantially increased. Additionally, a large number of dense dislocations in the grains, which greatly reduced the lattice thermal conductivity is induced. A high power factor of ≈26 mW cm${}^{-1}$ K${}^{-2}$ and low lattice thermal conductivity of ≈0.43 W m${}^{-1}$ K${}^{-1}$ at 823 K in Pb${}_{0.95}$Na${}_{0.04}$Te${}_{0.97}$Se${}_{0.03}$ is achieved. Ultimately, a high figure of merit, ZT ≈2.2, is obtained at 823 K in quaternary PbTe compound. The current findings not only demonstrate that the introduction of trace amounts of Se and Pb vacancies in the PbTe matrix can effectively enhance Na solubility and minimize thermal conductivity, attaining synergistic improvement in electrical and thermal properties, but also indicate that the synergistic effect of Pb vacancies with a specific dopant is an alternative approach for enhancing ZT. (© 2024 Wiley‐VCH GmbH)