Structural and thermoelectric properties of Cu3RETe3 (RE = Er, Ho, Tb) materials

A key challenge in thermoelectric materials development
is achieving low thermal conductivity without compromising
the electrical performance. Rare-earth tellurides, due to their
complex crystal chemistry and intrinsic defects, offer a pathway to
optimize these conflicting parameters. In this work, we investigated
the structural and thermoelectric properties of a series of ternary
rare-earth copper tellurides, Cu3RETe3 (RE = Er, Ho, Tb). Our
findings reveal that the specific rare-earth element plays a critical
role in determining the crystal structure of these compounds.
Notably, the Er- and Ho-containing phases predominantly
crystallize in the orthorhombic Pmn21 structure, whereas the Tb
analogue adopts a trigonal R-3 structure. Owing to this structural
difference, the Tb-based compound exhibits approximately twice
the effective mass and, correspondingly, a 2-fold increase in the Seebeck coefficient attributed to band convergence, as confirmed
by theoretical calculations. All materials exhibit intrinsically low lattice thermal conductivity, attributed to strong lattice
anharmonicity and point defect scattering, particularly pronounced in Cu3TbTe3. Hall effect and Seebeck measurements indicate ptype
semiconducting behavior with carrier concentrations on the order of 1020 cm−3. First-principles calculations show the presence
of strong electronic correlations, and GGA+U method is necessary to confirm semiconducting electronic structures and support
experimental trends in carrier mobility and Seebeck coefficient. Among the compounds, Cu3HoTe3 achieves the highest peak
thermoelectric figure of merit (ZT ≈ 0.9 at 873 K), while Cu3TbTe3 delivers the highest average performance (ZTave = 0.4 over the
temperature range of 298−873 K). These findings highlight the potential of Cu3RETe3 compounds as efficient rare-earth-based
thermoelectric materials for energy conversion applications.