Ultralow Thermal Conductivity and High Thermoelectric Performance in AgCuTe₁–ₓSeₓ through Isoelectronic Substitution

In this paper, we report a series of x polycrystalline AgCuTe₁–ₓSe samples with high thermoelectric performance. X-ray photoelectron spectroscopy data suggest the observation of Ag⁺, Cu⁺, Te²–, and Se²– states of Ag, Cu, Te, and Se. Meanwhile, the carrier concentration of the obtained p-type samples changes from 9.12 × 10¹⁸ to 0.86 × 10¹⁸ cm–³ as their carrier mobility varies from 698.55 to 410.12 cm²·V–¹·s–¹ at 300 K. Compared with undoped AgCuTe, an ultralow thermal conductivity is realized in AgCuTe₁–ₓSeₓ due to the enhanced phonon scattering. Ultimately, a maximum figure of merit (ZT) of ∼1.45 at 573 K and a high average ZT above 1.0 at temperatures ranging from room temperature to 773 K can be achieved in AgCuTe₀.₉Se₀.₁, which increases by 186% compared to that of the undoped AgCuTe (0.82 at 573 K). This work provides a viable insight toward understanding the effect of the Se atom on the lattice structure and thermoelectric properties of AgCuTe and other transition-metal dichalcogenides.