Ultralow Thermal Conductivity in Diamondoid Structures and High Thermoelectric Performance in (Cu_1–xAg_x)(In_1–yGa_y)Te₂

Abstract

Owing to the diversity of composition and excellent transport properties, the ternary I−III−VI 2 type diamond-like chalcopyrite compounds are attractive functional semiconductors, including as thermoelectric materials. In this family, CuInTe 2 and CuGaTe 2 are well investigated and achieve maximum ZT values of ∼1.4 at 950 K and an average ZT of 0.43. However, both compounds have poor electrical conductivity at low temperature, resulting in low ZT below 450 K. In this work, we have greatly improved the thermoelectric performance in the quinary diamondoid compound (Cu 0.8 Ag 0.2 )(In 0.2 Ga 0.8 )Te 2 by understanding and controlling the effects of different constituent elements on the thermoelectric transport properties. Our combined theoretical and experimental effort indicates that Ga in the In site of the lattice decreases the carrier effective mass and improves the electrical conductivity and power factor of Cu 0.8 Ag 0.2 In 1−x Ga x Te 2 . Furthermore, Ag in the Cu site strongly suppresses the heat transport via the enhanced acoustic phonon−optical phonon coupling effects, leading to the ultralow thermal conductivity of ∼0.49 W m −1 K −1 at 850 K in Cu 0.8 Ag 0.2 In 0.2 Ga 0.8 Te 2 . Defect formation energy calculations suggest intrinsic Cu vacancies introduce defect levels that are important to the temperature-dependent hole density and electrical conductivity. Therefore, we introduced extra Cu vacancies to optimize the hole carrier density and improve the power factor of Cu 0.8 Ag 0.2 In 0.2 Ga 0.8 Te 2 . As a result, a maximum ZT of ∼1.5 at 850 K and an average ZT of 0.78 in the temperature range of 400−850 K are obtained, which is among the highest in the diamond-like compound family.

Significant Increase of Electron Thermal Conductivity in Dirac Semimetal Beryllonitrene by Doping Beyond Van Hove Singularity

“…Determining the properties of 2D matter in the one‐atom‐thin limit is a current frontier of science. [ 1–18 ] One such emergent quantum phenomenon is the electronic transport through Dirac cones, which were first identified in graphene. [ 1–3 ] Close to the charge neutrality point, the graphene dispersion relation is linear and well described by the relativistic Dirac equation [ 4 ] with charge carriers as massless Dirac fermions.…”

Unconventional Doping Effect Leads to Ultrahigh Average Thermoelectric Power Factor in Cu3SbSe4‐Based Composites

“…a) The zT values and b) quality factor as a function of temperature for the Cu 3 SbSe 4 − x CuAlSe 2 ( x = 0, 2, 4, 6, 8, and 10 wt%) composites. c) PF avg of this work ( x = 4 and 8 wt%) compared with those of reported high‐performance p‐type thermoelectrics (CuIn/GaTe 2 [ 23,24,27,29,31,35,38 ] ) in the temperature range of 300–723 K. d) Comparison on average zT andPF avg of Cu 3 SbSe 4 − x CuAlSe 2 ( x = 4 and 8 wt%) composites and other copper‐based diamond‐like thermoelectrics. [ 23,24,27,29,31,34,35,38,57 ] …”

“…Most importantly, the PF max for the sample with x = 8 wt% reaches 19 µW cm −1 K −2 in the temperature range of 300–723 K, which is ≈58% larger than that of the Cu 2 InTe 1.99 Sb 0.01 +1 wt% ZnO. [ 27 ] Besides, in the temperature range of 300–723 K, for the sample with x = 4 wt% CuAlSe 2 has an average zT of 0.72, which is 26% larger than that of the reported highest value for Cu 3 SbSe 4 ‐based compounds [ 38 ] and is comparable to other state‐of‐the‐art copper chalcopyrites [ 23,24,27 ] containing tellurium (e.g., CuInTe 2 and CuGaTe 2 ) and even superior in the temperature range of 300–723 K.…”

“…Holding the advantages of consisting of earth‐abundant and environmental‐friendly elements, copper‐based diamond‐like compounds have been considered as promising TE materials, including CuInTe 2 , [ 22–27 ] CuGaTe 2 , [ 28–31 ] Cu 3 SbSe 4 , and so on. [ 32–39 ] The tellurium‐free compound Cu 3 SbSe 4 with a narrow band gap (≈0.3 eV), which is featured by high density of states effective mass m d * (≈1.5–2.0 m e ), has been investigated frequently in recent years.…”

Application of Materials Genome Methods in Thermoelectrics

“…The second leap in development occurred because of new concepts and technologies, such as phonon glass electron crystals (PGECs) (Rowe, 2018), nanotechnology (Shakouri, 2011), and energy band engineering (Capasso, 1987). Some new TE materials with complex structures have been discovered and their thermal and electric properties are greatly improved; these materials include skutterudites (Rogl et al, 2015), diamond-like compounds (Xie et al, 2021), half-Heuslers (Fu et al, 2015a), Cu 2 Se (Olvera et al, 2017), SnSe (Chang et al, 2018), and other materials. HTP calculations and ML have injected "new blood" into the discovery of highperformance TE materials in recent years and may lead to a third leap forward.…”