Influence of Ag substitution on thermoelectric properties of the quaternary diamond-like compound Zn2Cu3In3Te8

The quaternary diamond-like compounds, A2Cu3In3Te8 (A = Cd, Zn, Mn, Mg), are a new class of thermoelectric materials recently proposed by complex structure design. Among them, the Zn2Cu3In3Te8 compound possesses reasonable electrical transport properties but relatively high lattice thermal conductivity. Herein, the effects of Ag substitution on the phase stability and thermoelectric properties of Zn2Cu3In3Te8 compound are reported. It is revealed that only the In sites show an appreciable tolerance for Ag doping. Ag substitution at the In sites introduces extra holes and thus results in improved electrical transport properties. Furthermore, the introducing of Ag lowers the sound velocities and enhances the phonon scattering of the Zn2Cu3In3Te8 compound, which leads to a substantially reduction in lattice thermal conductivity. Finally, in virtue of the optimization in both electrical and thermal transport properties, the maximal zT value of Zn2Cu3In2.8Ag0.2Te8 sample reaches 0.62 at 823 K, which is 43% higher than the pristine sample.