Doping telluride for tuning the crystal structure and thermoelectric performance of copper selenide-based materials

The prototype phonon-liquid electron-crystal β-Cu${}_2$Se has been recognized as one of the top-performing thermoelectric materials due to its ultralow lattice thermal conductivity (κ). This paper reports the synthesis of Telluride-doped Bi${}_{0.001}$Cu${}_2$Se through the combination of ball milling and spark plasma sintering. The thermoelectric properties of the materials, encompassing electrical resistivity, Seebeck coefficient, and thermal conductivity within the temperature range of 300 K to 873 K, have been evaluated. The Bi${}_{0.001}$Cu${}_2$Se${}_{0.90}$Te${}_{0.10}$ sample exhibited a peak Seebeck coefficient of 192.6 µV/K, which is approximately 23.5% higher than that of the bulk Bi${}_{0.001}$Cu${}_2$Se alloy. Both Bi${}_{0.001}$Cu${}_2$Se and Bi${}_{0.001}$Cu${}_2$Se${}_{0.90}$Te${}_{0.10}$ demonstrated comparable high power factors of 1221.9 µWm${}^{-1}$ K${}^{-2}$ and 1223.6 µWm${}^{-1}$ K${}^{-2}$, attributed to their moderate electronic conductivity and Seebeck coefficient. The porous Bi${}_{0.001}$Cu${}_2$Se${}_{0.80}$Te${}_{0.20}$ samples exhibited a minimum thermal conductivity of 0.61${}^{-1}$ K${}^{-1}$ at 873 K, representing a reduction of up to 21.8% compared to the bulk Bi${}_{0.001}$Cu${}_2$Se alloy. This decrease in thermal conductivity can be attributed to the boundaries and defects formed during the spark plasma sintering process, as well as the porous nature of the samples. The figure of merit for the Bi${}_{0.001}$Cu${}_2$Se${}_{0.80}$Te${}_{0.20}$ was found to have a maximum value of approximately 1.49 at 873 K, primarily due to its significantly lower thermal conductivity.