Good stability and high thermoelectric performance of Fe doped Cu1.80S

Abstract

Copper sulfides have attracted great attention recently in the thermoelectric community due to the liquid-like behavior of Cu ions. Among the numerous copper sulfides, digenite Cu_1.80S has a poorer thermoelectric performance but better stability than the state-of-the-art binary copper sulfide Cu_1.97S. In this study, good stability and high thermoelectric performance were simultaneously obtained in Fe-doped Cu_1.80S. Because Fe ions will not form a concentration gradient under an external field to change the critical voltage, Fe-doped Cu_1.80S samples inherit the good stability of the pristine Cu_1.80S. The critical voltage for Cu_1.80Fe_0.064S is 0.16 V at 750 K, which has been the largest value reported so far. Likewise, the Fe dopants can significantly improve the thermoelectric performance by suppressing the too high electrical conductivity of Cu_1.80S. The peak dimensionless figure of merit (zT) for Cu_1.80Fe_0.064S is around 0.8 at 750 K, about four times that of Cu_1.80S. The average zT for Cu_1.80Fe_0.064S is 0.40 in 300–750 K, which is amongst the highest values in reported thermoelectric sulfides. Combining the good stability and high thermoelectric performance, the present Cu_1.80Fe_0.064S has great potential to be used in the application of waste heat harvesting in the middle temperature range.