Band manipulation for high thermoelectric performance in SnTe through heavy CdSe-alloying

Abstract

Convergence of L and Σ valence bands through alloying with monotellurides, has successfully realized the significant zT-enhancement in SnTe thermoelectrics. CdTe, as a solvend introducing Cd-substitution at Sn site, has been demonstrated theoretically and experimentally as an effective agent to reduce the energy difference between two valence bands. However, the low solubility of ∼3% for CdTe in SnTe limits the possibility for further zT-enhancement in SnTe, which motivates the existing efforts on increasing solubility of CdTe or exploring Cd-based solvend with higher solubility. Inspired by the solubility as high as 14% for CdSe in SnTe at 1050 K, this work focuses on the effect of CdSe on thermoelectric properties of SnTe. The converged valence bands induced by the heavy Cd-substitution, results in a significant increase in electronic performance. Moreover, CdSe-alloying would simultaneously introduce cation and anion point defects and boundary interfaces of CdSe precipitates, which leads to a strong phonon scattering and therefore a reduced lattice thermal conductivity of ∼0.8 W/m-K. As a result, the synergistic effect of electronic and thermal performances results in a peak zT as high as 1.1 at 850 K, demonstrating (SnTe)1-x(CdSe)x as the promising thermoelectric materials.