Weak electron-phonon coupling and enhanced thermoelectric performance in n-typePbTe-Cu${}_2$Se via dynamic phase conversion

This study investigates Ga-doped n-type PbTe thermoelectric materials and the dynamic phase conversion process of the second phases via Cu${}_2$Se alloying. Introducing Cu${}_2$Se enhances its electrical transport properties while reducing its lattice thermal conductivity (κ${}_{lat}$) via weak electron-phonon coupling. Cu${}_2$Te and CuGa(Te/Se)${}_2$ (tetragonal phase) nanocrystals precipitate during the alloying process, resulting in Te vacancies and interstitial Cu in the PbTe matrix. At room temperature, Te vacancies and interstitial Cu atoms serve as n-type dopants, increasing the carrier concentration and electrical conductivity from ≈1.18 × 10${}^{19}$ cm${}^{-3}$ and ≈1870 S cm${}^{-1}$ to ≈2.26 × 10${}^{19}$ cm${}^{-3}$ and ≈3029 S cm${}^{-1}$, respectively. With increasing temperature, the sample exhibits a dynamic change in Cu${}_2$Te content and the generation of a new phase of CuGa(Te/Se)${}_2$ (cubic phase), strengthening the phonon scattering and obtaining an ultralow κ${}_{lat}$. Pb${}_{0.975}$Ga${}_{0.025}$Te-3%CuSe exhibits a maximum figure of merit of ≈1.63 at 823 K, making it promising for intermediate-temperature device applications. (© 2022 Wiley‐VCH GmbH)