Abstract
Introduction of nonstoichiometry to AgSbTe2-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 Ag1−xSb1+xTe2+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 Ag1−xSb1+xTe2+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 ZTmax = 1.2 is observed at 610 K for the slowly cooled multi-phase sample Ag0.9Sb1.1Te2.1. Thermoelectric properties are repeatedly reproducible up to 490 K.
Highlights
Introduction of nonstoichiometry toAgSbTe2 -based materials is considered to be an effective way to tune thermoelectric properties to extrinsic doping
The only thermodynamically stable ternary phase in this system is the β phase (Ag1−x Sb1+x Te2+x, 0.08 < x < 0.41 [10]), which crystallizes in the NaCl structure type
Further investigations of the Ag-Sb-Te ternary system confirmed that the β phase is only stable in a limited temperature range (633 K < T < 847 K) and it decomposes into α
Summary
Chalcogenides that crystallize in the NaCl structure type (Fm3m), e.g., PbTe, PbSe or SnTe, belong to the best thermoelectric (TE) materials [1]. The only thermodynamically stable ternary phase in this system is the β phase (Ag1−x Sb1+x Te2+x , 0.08 < x < 0.41 [10]), which crystallizes in the NaCl structure type. Further investigations of the Ag-Sb-Te ternary system confirmed that the β phase is only stable in a limited temperature range (633 K < T < 847 K) and it decomposes into α Single-phase alloy with the nominal composition Ag0.875 Sb1.125 Te2 We decided to answer two questions: (i) what is the real stability range of the β phase within the pseudobinary Sb2 Te3 -Ag2 Te system, (ii) whether tuning of thermodynamic stability and TE performance is possible by deviating composition from the stoichiometric Ag1.0 Sb1.0 Te2. We investigated the influence of thermal treatment on thermodynamic stability and TE performance of alloys. Our experiments and following conclusions concern the Sb2 Te3 -Ag2 Te pseudobinary system only, some of them can be applicable to the Ag-Sb-Te ternary system as well
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