Thermoelectric Properties and Thermal Stability of BiCuSeO

Although BiCuSeO has become of interest as a high performance thermoelectric material, it has been reported to be unstable in air above 548 K. However, the details of the thermal degradation of BiCuSeO have not yet been determined. In this study, the time dependence of the thermoelectric properties of BiCuSeO at 550 K was assessed along with the accompanying thermal degradation behavior. Variations in ρ and α over time at 550 K were determined using the direct current four-terminal method and small temperature difference method, respectively. In addition, the crystalline phases of the specimen after thermoelectric measurements were identified by x-ray diffraction (XRD) analysis, and the surface chemical states were analyzed by x-ray photoelectron spectroscopy (XPS). The results of thermoelectric property measurements over time showed that ρ abruptly increased between 135 min and 182 min then decreased from 182 min to 210 min, while the value of α exhibited the opposite trend. XPS and XRD data suggested that BiCuSeO was pyrolyzed upon heating at 550 K for 6 h in air. In contrast, thermogravimetric analysis demonstrated that BiCuSeO was stable below 800 K under inert gas flow, thus the pyrolysis observed at 550 K was the result of reaction with atmospheric oxygen.