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

Abstract

Introduction of nonstoichiometry to AgSbTe 2 -based materials is considered to be an effective way to tune thermoelectric properties similarly to extrinsic doping. To prove this postulate, a systematic physicochemical study of the Ag 1−x Sb 1+x Te 2+x alloys (0 ≤ x ≤ 0.4) was performed. In order to investigate the influence of the cooling rate after synthesis on phase composition and thermoelectric performance, slowly cooled and quenched Ag 1−x Sb 1+x Te 2+x alloys (x = 0; 0.1; 0.17; 0.19; 0.3; 0.4) were prepared. Single-phase material composed of the β phase (NaCl structure type) was obtained for the quenched x = 0.19 sample only. The other alloys must be regarded as multi-phase materials. The cooling rate affects the formation of the phases in the Ag-Sb-Te system and influences mainly electronic properties, carrier mobility and carrier concentration. The extremely low lattice thermal conductivity is an effect of the mosaic nanostructure. The maximal value of the figure of merit ZT max = 1.2 is observed at 610 K for the slowly cooled multi-phase sample Ag 0.9 Sb 1.1 Te 2.1 . Thermoelectric properties are repeatedly reproducible up to 490 K.

Phase Equilibria and Thermoelectric Properties in the Pb–Ga–Te System in the Vicinity of the PbGa6Te10 Phase

“…However, Li 2 Ga 6 Te 10 and Na 2 Ga 6 Te 10 are examples of compounds with M + ions (Li + , Na + ) in which all octahedral voids are occupied . The substitution of atoms in the structural voids can significantly modify the thermal and transport properties of such types of materials. − …”

Phase Equilibria in the Ag2Te-PbTe-Sb2Te3 System and Thermodynamic Properties of the (2PbTe)1-x(AgSbTe2)x Solid Solutions

“…Recent works are devoted to the search for optimal compositions of this nonstoichiometric phase, which exhibits a high thermoelectric figure of merit. 46,47 The eutectic of the Ag 2 Te-Sb 2 Te 3 system crystallizes at 70 mol% Ag 2 Te and 817 K. 38 The phase diagram of the PbTe-Sb 2 Te 3 boundary system reported in, 48 was characterized by formation only ternary compound Pb 2 Sb 6 Te 11 , at approximately the eutectic composition on peritectic reaction at 860 K. Shelimova et al, 49 showed formation in this system also PbSb 2 Te 4 and PbSb 4 Te 7 compounds with a layered structure. However, further studies on this system, 50,51 have not confirmed the last compounds.…”

Charge Compensation Modulation of the Thermoelectric Properties in AgSbTe2 via Mn Amphoteric Doping

“…24−27 However, in some special systems, such as AgSbTe 2 , due to the intrinsic high σ and low κ l , 28−30 the κ e /κ total ratio is already high enough that when positive doping is applied, though the PF is optimized, the increase in κ e can offset the decrease in κ l and make the κ total increase with the increase of PF, which limits the improvement of thermoelectric performance and may even degrade the final ZT value. 31 This issue urges us to adopt new doping modes that can improve PF while ensuring the effective reduction of κ total . In this regard, the amphoteric doping method that combines positive dopant with additional negative dopant to adjust and optimize the carrier concentration may serve as a satisfactory solution.…”

“…Contrarily, the negative doping mode refers to inverse element doping which has a purpose to decrease the major carrier concentration through charge compensation with the introduced minor carriers. , It is worth noting that, according to the Wiedemann–Franz law, κ e = L σ T , which indicates that in positive doping the κ e will increase with σ, which is detrimental to the promotion of ZT performance. Fortunately, in most cases, due to the low proportion of κ e in the total thermal conductivity (κ total ), this tiny increase in κ e is always compensated by the large decrease in κ l owning to the strong defect-phonon scattering, which finally gives rise to a reduction of κ total . − However, in some special systems, such as AgSbTe 2 , due to the intrinsic high σ and low κ l , − the κ e /κ total ratio is already high enough that when positive doping is applied, though the PF is optimized, the increase in κ e can offset the decrease in κ l and make the κ total increase with the increase of PF, which limits the improvement of thermoelectric performance and may even degrade the final ZT value . This issue urges us to adopt new doping modes that can improve PF while ensuring the effective reduction of κ total .…”