Weak Electron–Phonon Coupling and Enhanced Thermoelectric Performance in n-type PbTe–Cu_2Se via Dynamic Phase Conversion

摘要

This study investigates Ga-doped n-type PbTe thermoelectric materials andthe dynamic phase conversion process of the second phases via Cu_2Sealloying. Introducing Cu_2Se enhances its electrical transport properties whilereducing its lattice thermal conductivity (κ_(lat)) via weak electron–phononcoupling. Cu_2Te and CuGa(Te/Se)_2 (tetragonal phase) nanocrystals precipitateduring the alloying process, resulting in Te vacancies and interstitial Cu inthe PbTe matrix. At room temperature, Te vacancies and interstitial Cu atomsserve as n-type dopants, increasing the carrier concentration and electricalconductivity 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 exhibitsa dynamic change in Cu_2Te content and the generation of a new phaseof CuGa(Te/Se)_2 (cubic phase), strengthening the phonon scattering andobtaining an ultralow κ_(lat). Pb_(0.975)Ga_(0.025)Te-3%CuSe exhibits a maximum figureof merit of ≈1.63 at 823 K, making it promising for intermediate-temperaturedevice applications.