Silver Atom Off-Centering in Diamondoid Solid Solutions Causes Crystallographic Distortion and Suppresses Lattice Thermal Conductivity

Abstract

The class I−III−VI 2 diamondoid compounds with tetrahedral bonding are important semiconductors widely applied in optoelectronics. Understanding their heat transport properties and developing an effective method to predict the diamondoid solid solutions' thermal conductivity will help assess their impact as thermoelectrics. In this work, we investigated in detail the heat transport properties of CuGa 1−x In x Te 2 and Cu 1−x Ag x GaTe 2 and found that in the Ag-alloyed solid solutions, the Ag atom off-centering effect results in crystallographic distortion and extra strong acoustic−optical phonon scattering and an extremely low lattice thermal conductivity. Moreover, we integrate the alloy scattering and the off-centering effect with the crystallographic distortion parameter to develop a modified Klemens model that predicts the thermal conductivity of diamondoid solid solutions. Finally, we demonstrate that Cu 1−x Ag x GaTe 2 solid solutions are promising p-type thermoelectric materials, with a maximum ZT of 1.23 at 850 K for Cu 0.58 Ag 0.4 GaTe 2 .

Microstructural iterative reconstruction toward excellent thermoelectric performance in MnTe

“…5 In medium-temperature areas, the study of toxic conventional PbTe has numerous limitations, 6,7 and other promising compounds, such as GeTe, 8,9 SnTe, 10,11 SnSe, 12 Half-Heusler, 13 CoSb 3 , 14,15 and Cu 2 (Se,S) 16 etc., have been highly anticipated. Armed with the modern band engineering theory and defect engineering methods, [17][18][19] numerous middle-temperature specimens have been published. However, application attempts are still in their infancy mainly because the improvement in transport properties has occurred at the expense of other significant aspects, 20,21 such as stability, machinability, or reproducibility, resulting in a lack of generating modules.…”

“…, have been highly anticipated. Armed with the modern band engineering theory and defect engineering methods, 17–19 numerous middle-temperature specimens have been published. However, application attempts are still in their infancy mainly because the improvement in transport properties has occurred at the expense of other significant aspects, 20,21 such as stability, machinability, or reproducibility, resulting in a lack of generating modules.…”

Stepwise Alloying in Liquid-like Solid Solutions to Achieve Crystallographic Distortion for Regulating Thermoelectric Transport Behavior

“…For the relevant parameters, κ was easily adjusted in comparison with the other parameters, and it can be optimized by microstructure and stepwise alloying design . Illuminated by the idea of “crystallographic distortion” of diamondoid solid solutions, the stepwise alloying strategy is expected to create a different approach to depress thermal conductivity in solid solutions. , Theoretically, stepwise alloying strategies could adjust lattice thermal conductivity; for example, carrier pocket engineering, interfacial effects, and entropy engineering can synergistically tune the intrinsic phonon scattering. The stepwise alloying strategies have been widely applied in previous study, such as (GeTe) 1– x (AgSnSe 2 ) x , AgMnSbTe 3 , GeSe, Pb 0.89 Sb 0.012 Sn 0.1 Se 0.5 Te 0.25 S 0.25 , etc.…”

Enhancing Thermoelectric Performance of CuInTe2 via Trace Ag Doping at Indium Sites

“…This structure imparts pristine CuInTe 2 with increased S ( S ≈ 100 to 500 μV K –1 at 300 K) − and a relatively high electrical resistivity (ρ ≈ 1 × 10 4 Ω –1 m –1 at this temperature), attributing to only a moderate PF. Simultaneously, CuInTe 2 exhibits a considerably higher κ T (κ T ≈ 6–9 W m –1 K –1 at 300 K) than additional most advanced thermoelectric materials. − Numerous strategies have been proposed to manipulate the thermoelectric properties of CuInTe 2 . For instance, chemical composition doping, i.e., replacing Cu/In at the cation site (e.g., Ag, Hg, Cd, Mn, and Ni) or Te at the anion site (e.g., S), was demonstrated to be an effective approach for optimizing the thermoelectric performance by means of modulating the carrier concentration n .…”

“…Although Ag doping at In sites does not substantially modify the electronic structures near the edge of the VB, it can manipulate the n to enhance the thermoelectric ZT of CuInTe 2 . Moreover, owing to the crystallographic distortion, Ag off-centering effect, and additional strong acoustic–optical phonon scattering, extremely low κ L can be achieved for Ag-alloyed diamondoid solid solutions …”