Thermal stability study of Cu1.97Se superionic thermoelectric material

With the development of high-temperature thermoelectric materials, especially for the superionic copper selenide (Cu2-xSe), the thermal stability and cycling thermoelectric performance have become a great concern recently. Here we demonstrate that the excellent repeatability of the thermal cycling data of the simple Cu-Se binary system can be obtained. The thermal stability was systematically studied via measuring the thermal-cycling thermoelectric performances of Cu1.97Se samples with different rates of Se evaporation by adopting a simple and controllable method, i.e., a conventional solid-state sintering method. The samples fabricated using the conventional sintering method exhibited the optimized figure of merit of 0.8 at 800 K with very good thermal repeatability and stability from 400 K to 800 K. The results indicated that the conventional sintering method can also be adopted to fabricate the materials with satisfied thermoelectric performance. It was found that the repeatability of thermal cycling data is directly related to the sintering temperature and indirectly associated to the evaporation of Se. The Cu1.97Se samples sintered at low temperature experienced less evaporation of Se with good thermal repeatability, while they exhibited relatively low thermoelectric performance due to the high carrier concentration. Although the samples sintered at high temperature show a large variation on the thermal cycling performance, the repeatability could be improved by the further annealing process, which reveals that the good thermal stability of thermoelectric materials can be obtained via the post-treatment.