High-Performance and Stable (Ag, Cd)-Containing ZnSb Thermoelectric Compounds

Binary Zn-Sb-based compounds, ZnSb and Zn₄Sb₃, are promising thermoelectric (TE) materials because they are low-cost and earth-abundant. However, for a long time, their real applications have been limited by the low TE figure-of-merit (zT) of ZnSb and poor thermodynamic stability of Zn₄Sb₃. In this study, we successfully integrate both high zT and good stability in (Ag, Cd)-containing ZnSb compounds. Alloying Cd in ZnSb greatly suppresses the lattice thermal conductivity to a minimum value of 0.97 W K^-1 m^-1 at 300 K, while doping Ag significantly enhances the power factor to a peak value of 17.7 μW cm^-1 K^-2 at 500 K and reduces the bipolar thermal conductivity. As a result of the simultaneously optimized electrical and thermal transport, a peak zT of 1.2 is achieved for Zn_0.698Ag_0.002Cd_0.3Sb at 600 K, which is comparable with the best values reported for Zn₄Sb₃-based compounds. Moreover, a current stress test confirms that introducing Ag and Cd does not degrade the good stability of ZnSb under an electric field. The phase composition and thermoelectric performance of Zn_0.698Ag_0.002Cd_0.3Sb are not changed even under a high current density of 50 A cm^-2, showing much better stability than Zn₄Sb₃. This study would accelerate the real application of ZnSb-based compounds in the field of waste heat harvesting.