Thermoelectricity and localized f-band control by dp-hybridization on the Ce_1-x Cu_x Se₂ compounds

We measured the temperature-dependent thermal conductivity κ(T), Seebeck coefficient S(T), and electrical resistivity ρ(T) of the polycrystalline Ce_1-x Cu_x Se₂ (x=0.0, 0.1, 0.2, and 0.3) series compounds. The high temperature thermoelectric property measurements of Ce_0.9 Cu_0.1 Se₂ have shown that the maximum thermoelectric figure-of-merit (ZT) reached up to 0.18 at 800 K due to the large Seebeck coefficient (S≈344 μV/K) and relatively low thermal conductivity (κ=0.71 W m^-1 K^-1). By increasing the Cu-doping concentration (x≥0.2), the Z_T is lowered mainly due to increasing the thermal conductivity. From the band structure calculation, the high Seebeck coefficient for the Ce_0.9 Cu_0.1 Se ₂ compound is attributed to the localized Ce f-band near the Fermi level due to Cu d-and Se p-orbital hybridization. The localized f-band has been shifted to a higher energy from the Fermi level with increased Cu-doping concentration, which is consistent with the decrease in the Seebeck coefficient. This research proposes that the orbital hybridization control on the layered structure rare-earth dichalcogenides is promising for high ZT thermoelectric materials development.