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

A new group of thermoelectric materials, trigonal and tetragonal XYZ₂ (X, Y: rare earth or transition metals, Z: group VI elements), the prototype of which is TmAgTe₂, 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 TmAgTe₂ at 600 K). Among approximately 500 chemical variants of XYZ₂ explored, many candidates with good stability and favorable electronic band structures (with high band degeneracy leading to high power factor) are presented. Trigonal TmAgTe₂ 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 TmAgTe₂ is approximately 0.35, and is limited by a low hole concentration (∼10¹⁷ 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 TmAgTe₂.