Syntheses, structures, and thermoelectric properties of ternary tellurides: RECuTe2 (RE = Tb–Er)

Abstract

In this work, four ternary rare-earth copper tellurides with a general formula RECuTe₂ (RE = Tb, Dy, Ho, Er) were successfully synthesized by a conventional high-temperature solid-state reaction of the elements. These isostructural materials adopted a known TmCuTe₂-structure type and contained a 2D honeycomb-like layer built up from CuTe₄ tetrahedral building units along the c-axis, with RE³⁺ located in layers. Moreover, all of them show a first order structure phase-transition, from the low-temperature-phase (LTP, space group: Pm1) to the high-temperature-phase (HTP, space group: P), due to the Cu atom's re-distribution on the covalent CuTe₄-based layer substructure. It is interesting to note the influence of the electronegativity of the constituent rare-earth metals on thermoelectric (TE) properties, e.g., the Seebeck coefficient (S) values decrease while the electrical conductivity (σ) and thermal conductivity (k) values increase with increasing electronegativity for a given RE. Consequently, TbCuTe₂ showed the highest dimensionless figure-of-merit ZT value of 1.0 at 750 K in the present RECuTe₂ systems, which is a promising TE candidate for medium temperature applications.