Polarity switching via defect engineering in Cu doped SnSe0.75S0.25 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.

Keywords

• Tin selenide
• phonon scattering
• solid solution
• defect engineering
• thermoelectric