Ultrahigh Thermoelectric Figure of Merit and Enhanced Mechanical Stability of p-type AgSb_1–xZn_xTe₂

Abstract

High-performance thermoelectric materials are desirable in the lower-medium temperature range (450–650 K) for low-grade waste heat recovery. We report a thermoelectric figure of merit (zT) of 1.9 at 585 K in p-type AgSb1–x Zn x Te2, which is the highest value measured among the p-type materials in the 450–650 K range. A high average thermoelectric figure of merit (zTavg) of 1.3 is achieved in AgSb0.96Zn0.04Te2. Moreover, the AgSb1–x Zn x Te2 sample exhibits a hardness value of ∼6.3 GPa (nanoindentation), which is significantly higher than that of the pristine AgSbTe2. Substitution of Zn in AgSbTe2 suppresses the formation of intrinsic Ag2Te impurity phases, which indeed increases the thermal and mechanical stability. The lattice thermal conductivity for AgSb1–x Zn x Te2 samples is reasonably reduced compared to that of the pristine AgSbTe2 because of the significant solid solution point defect phonon scattering. Aliovalent Zn2+ doping in Sb3+ sites in AgSbTe2 increases the p-type carrier concentration, which boosts the electrical conductivity of AgSb1–x Zn x Te2.

Thermal Stability and Tuning of Thermoelectric Properties of Ag1−xSb1+xTe2+x (0 ≤ x ≤ 0.4) Alloys

“…Slowly cooled alloys with x = 0.1 and x = 0.17 exhibit the highest TE performance, showing ZT values of 1.2 and 1.1 at 610 K, respectively. It is clear that high ZT values in Ag 1−x Sb 1+x Te 2+x alloys can also be obtained without extrinsic doping as reported previously [2][3][4][5][6]. All samples reveal lack of long-term stability, which causes degradation of the β phase and the TE performance, in agreement with the phase diagram of the Ag-Sb-Te system.…”

“…Numerous studies, concerning the TE performance of AgSbTe 2 -alloys with various dopants, reported very large values of TE figure of merit ZT > 1.3 [2][3][4][5][6]. That is mainly due to the extremely low thermal conductivity of the material in the range of 0.5-0.7 W·m −1 ·K −1 [7][8][9].…”

“…Pseudobinary phase diagrams of the Sb 2 Te 3 -Ag 2 Te system were elaborated separately in [10,19] (Figure 1). …”

Evaluation of Thermoelectric Properties of Ag0.366Sb0.558Te

“…With years of development, an extraordinary zT for AgSbTe 2 has been realized. [36,37,[46][47][48][49][50][51][52][53][54] It should be noted that stoichiometric AgSbTe 2 has been reported to be thermodynamically unstable, and partial decomposition into Ag 2 Te and Sb 2 Te 3 would be observed during thermal cycling. [55][56][57] Moreover, phase transition of Ag 2 Te at ≈418 K (if exist) leads to a detrimental effect on the stability of thermoelectric devices.…”

Studies on n- and p-type metal oxide compounds for thermoelectric device fabrication

“…There are several thermoelectric materials reported in the literature with ZT ∼ 1, such as AgSbTe 2 , PbTe, SnTe, SiGe, etc. Recently, there were some interesting reports where ZT > 1 was reported for similar compounds [6][7][8]. However, their applicability is not feasible till now due to various reasons, such as limited range of temperatures, difficulty in preparing materials in large quantities, toxicity of elements, degradation as a function of time or temperature, etc.…”