Altering the high-temperature stability and thermoelectric properties of Cu1.8S thermoelectric materials by Se incorporation

Thermoelectric materials based on Cu 1.8 S are not hampered by electric-field-driven degradation in real applications, but their high-temperature applications are problematic owing to their tendency to oxidize or spontaneously decompose. Here, we reveal that Cu 1.8 S powder is gradually oxidized to form a mixture of Cu 2 O, Cu(SO 4 ), and Cu 2 O(SO 4 ) at high temperatures under air. Although a dense oxide film is formed on the surface of the sintered Cu 1.8 S block at high temperature, hindering the oxidation process , the brittle oxide film fails to inhibit the spontaneous decomposition of the Cu 1.8 S block into the Cu 1.96 S phase and S vapor at high temperatures. Thus, Cu 1.8 S thermoelectric materials are unsuitable for applications above 300 °C in air. To address this issue, we partially replaced S atoms with Se; the sintered Cu 1.8 S 0.8 Se 0.2 blocks exhibited significantly increased anti-oxidation and anti-decomposition capacities in air. In addition, we found that the thermoelectric figure of merit of the sintered Cu 1.8 S 0.8 Se 0.2 block was 47% higher than that of traditionally prepared, pure Cu 1.8 S at 450 °C.