Polarity switching via defect engineering in Cu doped SnSe_0.75S_0.25 solid solution for mid-temperature thermoelectric applications

Abstract Solid solution SnSe 0.75 S 0.25 has potential to improve thermoelectric performance via ultra-low thermal conductivity as compared to the pristine SnSe which originates from phonon scattering due to disordered atoms of selenium (Se) and sulfur (S). SnSe 0.75 S 0.25 and Cu-doped SnSe 0.75 S 0.25 compounds were prepared via high energy ball milling and pelletized by a spark plasma sintering (SPS) process. Dislocation and point defects were successfully introduced by SnSe 0.75 S 0.25 . The existence of S in the Se site induced mass fluctuation which favors high-frequency phonon scattering. This leads to an impressively ultra-low thermal conductivity ( κT ) value of 0.258 W mK −1 at 753 K for SnSe 0.75 S 0.25 . Next, the Cu dopant was selected to enhance the electrical conductivity, which improved from 514.44 S m −1 (SnSe 0.75 S 0.25 ) to 725.08 S m −1 for Sn 0.98 Cu 0.02 Se 0.75 S 0.25 at 738 K. Interestingly, the Cu dopant induced nanoprecipitates of Cu 2 Se inside the grains, which further strengthens the phonon scattering. The Cu 2 Se nanoprecipitates and various defects at the grain boundaries contributed to a lower κT of 0.295 W mK −1 at 753 K for a Sn 0.94 Cu 0.06 Se 0.75 S 0.25 sample. Moreover, the maximum figure of merit of ( ZT) ∼0.19 at 738 K was attained for the Sn 0.98 Cu 0.02 Se 0.75 S 0.25 sample.