Ternary Compounds Cu3RTe3 (R = Y, Sm, and Dy): A Family of New Thermoelectric Materials with Trigonal Structures.

In this work, we report a series of Cu3RTe3 (R = Y, Sm, and Dy) ternary compounds with a trigonal structure (R3̅) as a family of new thermoelectric materials. First-principles calculations show that Cu3RTe3 (R = Y, Sm, and Dy) compounds are semiconductors with similar band structures and moderate band gaps (0.69-0.82 eV). The synthesized polycrystalline Cu3RTe3 (R = Y, Sm, and Dy) compounds possess moderate carrier concentrations (0.8-2.2 × 1020 cm-3) and density-of-state effective masses (around 1.1 me), yielding decent electrical transport performance. Furthermore, intrinsically low lattice thermal conductivities, below 1 W m-1 K-1 at 300-900 K, originating from the heavy average atomic masses and large number of atoms in the unit cell, are observed for Cu3RTe3 (R = Y, Sm, and Dy). Finally, Cu3DyTe3 demonstrates a peak dimensionless figure of merit of 0.9 at 900 K, which is among the highest reported for the Cu/Ag-based tellurides.