Computational and experimental investigation of TmAgTe2 and XYZ2 compounds, a new group of thermoelectric materials identified by first-principles high-throughput screening

Abstract

Promising thermoelectric materials ( XYZ ₂) with high band degeneracy and low thermal conductivity.

A new group of thermoelectric materials, trigonal and tetragonal XYZ ₂ ( X, Y: rare earth or transition metals, Z: group VI elements), the prototype of which is TmAgTe ₂, is identified by means of high-throughput computational screening and experiment. Based on density functional theory calculations, this group of materials is predicted to attain high zT ( i.e. ∼1.8 for p-type trigonal TmAgTe ₂ at 600 K). Among approximately 500 chemical variants of XYZ ₂ explored, many candidates with good stability and favorable electronic band structures (with high band degeneracy leading to high power factor) are presented. Trigonal TmAgTe ₂ has been synthesized and exhibits an extremely low measured thermal conductivity of 0.2–0.3 W m ⁻¹ K ⁻¹ for T > 600 K. The zT value achieved thus far for p-type trigonal TmAgTe ₂ is approximately 0.35, and is limited by a low hole concentration (∼10 ¹⁷ cm ⁻³ at room temperature). Defect calculations indicate that Tm _Ag antisite defects are very likely to form and act as hole killers. Further defect engineering to reduce such X _Y antisites is deemed important to optimize the zT value of the p-type TmAgTe ₂.