The efficiency of a thermoelectric (TE) device largely depends on the dimensionless figure of merit zT = S 2 σ T /κ, where S is the Seebeck coefficient, σ is the electrical conductivity, κ is the thermal conductivity, and T is the temperature. A route to achieving higher zT is through the reduction of κ. Since materials with low κ are desired, many studies have been dedicated to discovering novel low-κ materials for TE applications. Zhu et al. combined graph neural networks and random forest approaches to identify rare-earth chalcogenides as materials with low lattice thermal conductivity (κ L ), in agreement with known high-performing TE materials. La 3-x Te 4 , which has been extensively studied for high-temperature TE applications, forms a defected Th 3 P 4 structure type due to the valence imbalance of stoichiometric La 3 Te 4 . The high TE performance of La 3-x Te 4 partly stems from synergistic effects of light and heavy bands leading to overall advantageous electrical transport properties, as well as enhanced phonon scattering from La vacancies. Similar materials, such as Pr 3-x Te 4 , 20,21 Nd 3-x Te 4 , and La 3-x S 4 23,24 also exhibit low κ and high TE performance, likely due to the high degree of phonon scattering from the cation vacancies. Inspired by this chemical space of materials, the valence-balanced Sc 2 Te 3 was synthesized and found to have κ < 2 W/mK. Due to the prevalence of rare-earth chalcogenide TE materials, it is, therefore, natural to ask if there are other potentially high-performing TE materials within this chemical space. Zhu et al. identified Y 2 Te 3 as a low-κ L material with promising TE performance in their preliminary investigations. The ora Northwestern University, Evanston, IL 60208. b Thermal Energy Conversion Materials Group, Jet Propulsion Laboratory/California Institue of Technology, Pasadena, CA 91109. c Colorado School of Mines, Golden, CO 80401. * E-mail: MichaelToriyama2024@u.northwestern.edu, pgorai@mines.edu † Electronic supplementary information available. thorhombic crystal structure of Y 2 Te 3 (space group Fddd, Figure ) can be understood as a rock-salt derived structure with ordered cation vacancies, which is isostructural with the orthorhombic polymorph of Sc 2 Te 3 . The vacancy-ordered structures of Y 2 Te 3 and Sc 2 Te 3 are related to that of rhombohedral Sb 2 Te 3 , as evidenced by their phase transitions in phase-change memory alloys. Specifically, the structural relationship can be understood as a gathering of the ordered vacancies to form a van der Waals gaps in the rhombohedral Sb 2 Te 3 structure, similar to the phase transition mechanism of Ge 2 Sb 2 Te 5 . Therefore, it is not surprising that layered structures such as Sb 2 Te 3 and Bi 2 Te 3 , which are derived from rock-salt like structures, as well as Ge 2 Sb 2 Te 5 , 30 are well-known TE materials.