Remarkable Improvement of Thermoelectric Performance in Ga and Te Cointroduced Cu3SnS4.

Abstract

Ternary sulfide Cu3SnS4 (CTS) receives growing interest in photocatalytic and gas sensing applications; however, limited attention has been paid to the application in thermoelectrics in virtue of its intrinsic high carrier concentration. In this work, a high figure of merit of Ga (ZT) and Te cointroduced CTS with the composition of (Cu3SnS4)1-x(Ga2Te3)x (x = 0.105) has been realized via synergistic optimization of the electronic and thermal transport properties. The incorporation of Ga into CTS results in a downshift of both the conduction and valence bands, which effectively promotes the active hybridization of Sn 5s and S 3p orbitals near the Fermi level (EF) and optimizes the carrier concentration. In the meantime, the lattice thermal conductivity (κL) generally decreases on account of the local internal distortion induced by Ga(Te) substitution at the Cu(S) site. Moreover, the phonon transport is greatly suppressed above ∼725 K attributed to the melting of the second-phase Te on the grain boundaries. Consequently, the highest ZT value of ∼0.96 is obtained at 798 K. This value is ∼3.6 times that of the pristine CTS and ranks the highest in the CTS system to date.