Silver vacancy concentration engineering leading to the ultralow lattice thermal conductivity and improved thermoelectric performance of Ag1-xInTe2

Abstract

AgInTe2 compound has not received enough recognition in thermoelectrics, possibly due to the fact that the presence of Te vacancy (VTe) and antisite defect of In at Ag site (InAg) degrades its electrical conductivity. In this work, we prepared the Ag1-xInTe2 compounds with substoichiometric amounts of Ag and observed an ultralow lattice thermal conductivity (κL = 0.1 Wm−1K−1) for the sample at x = 0.15 and 814 K. This leads to more than 2-fold enhancement in the ZT value (ZT = 0.62) compared to the pristine AgInTe2. In addition, we have traced the origin of the untralow κL using the Callaway model. The results attained in this work suggest that the engineering of the silver vacancy (VAg) concentration is still an effective way to manipulate the thermoelectric performance of AgInTe2, realized by the increased point defects and modified crystal structure distortion as the VAg concentration increases.

Origin of the Distinct Thermoelectric Transport Properties of Chalcopyrite ABTe2 (A = Cu, Ag; B = Ga, In)

“…[33,[46][47][48] Concerning the electrical conductivity at room temperature, CuGaTe 2 and CuInTe 2 [46,47,49] possess electrical conductivities of about 2.1 × 10 3 and 4.1 × 10 3 S m −1 , respectively, while much lower electrical conductivities of around 0.35 and 4.8 S m −1 are obtained for AgGaTe 2 and AgInTe 2 , [50,51] respectively. For the thermal conductivity at 300 K, AgGaTe 2 and AgInTe 2 [50,51] exhibit thermal conductivities of 1.77 and 0.92 W m −1 K −1 , respectively, whereas the thermal conductivities are 7.40 and 6.60 W m −1 K −1 for CuGaTe 2 and CuInTe 2 , [46,47] respectively. In light of the isoelectronic substitution between Ag and Cu along with Ga and In, the origin of such discrepancies in both electrical and thermal transport properties is unknown and worth investigation.…”

Computationally Guided Synthesis of High Performance Thermoelectric Materials: Defect Engineering in AgGaTe2

“…This behavior was not observed in Ag 0.95 GaTe 2 , [ 21 ] but it can be observed in the AgInTe 2 ‐based systems. [ 54 ] We noted that in AgGa 0.93 Te 2 system [ 20 ] only temperature range of 500 to 900 K has been reported and the same temperature‐dependent behavior is found in the present study, that is, the value of α will decrease as the temperature increases from around 500 to 660 K; while the value of α will increase as the temperature increases from around 660 to 900 K. The possible explanation to the abnormal temperature dependence is the presence of order‐disorder transitions at about 660 K. [ 55–57 ] At around ≈660 K, the partial chalcopyrite structure (assumed to be the α phase) is transited to sphalerite structure (β phase) due to the Ag–In(Ga) antisite occupancy starting at the critical temperatures. [ 36 ] The order–disorder transformation was also observed in the ZnTe‐doped CuInTe 2 system.…”

“…[ 51 ] The detailed explanation of the transition is given in ref. [ 54 ]. It is noted that the lattice parts at high temperatures are low compared to those of AgGa 0.93 Te 2 , [ 20 ] and the κ L value at x = 0.15 is only 0.08 WK −1 m −1 at ≈850 K, less than a half that of AgGa 0.93 Te 2 (0.18 WK −1 m −1 ), [ 20 ] while the κ L value of AGT is 0.27 WK −1 m −1 , comparable to the reported value 0.26 WK −1 m −1 .…”

“…Combined with the three parameters (α, σ, κ), we attain the dimensionless figure of merit (ZT) values, as shown in Figure 4d, where the highest ZT value is 1.44 for Ag 0.85 Ga 1− x In x Te 2 ( x = 0.15) at ≈850 K. This value is about a 43% enhancement compared to ≈1.05 for AgGa 0.93 Te 2 , [ 20 ] and stands the highest in the AgGaTe 2 family so far. Also, this performance can be compared to other p‐type ternary chalcopyrite‐based systems, such as CuGaTe 2 (ZT = 1.2–1.51) [ 10,59,60 ] and CuInTe 2 (ZT = 1.47–1.65), [ 61–64 ] but it is much higher than those of AgInTe 2 ‐based materials (ZT = 0.62 at 814 K; 0.07 at 600 K), [ 54,65 ] indicating that the presence of the Ag vacancy and In substitution is vital to improve the TE performance of AGT. An inset in Figure 4d presents the PF of the materials.…”

Indium Chalcogenide Nanomaterials in the Forefront of Recent Technological Advancements

“…Ternary analogues of indium tellurides also find use in thermoelectric applications, such as copper indium telluride (CuInTe 2 ) and silver indium sulfide (AgInTe 2 ). The thermoelectric properties of the former have recently been reported to be enhanced by doping with manganese [65], while for the latter, adjusting only the silver concentration x (in Ag 1-xInTe 2 ) was sufficient [66]. The interesting properties of another ternary material potassium indium telluride (KInTe 2 ), for the first time, have been recently predicted and investigated through theoretical first-principle calculations [67]; preliminary studies suggest the material is a semiconductor with an indirect energy band gap.…”