Abstract
In order to systematize the knowledge on thermodynamic stability and thermoelectric properties of AgSbTe2-based alloys, several experiments examining the influence of thermal treatment on their structural and thermoelectric properties were performed. Samples with a nominal composition of AgSbTe2 and AgSbTe1.98Se0.02 were prepared and then annealed in various temperature conditions. It was confirmed that Ag1−xSb1+xTe2+x (β phase) is the only thermodynamically stable ternary compound in the Ag2Te-Sb2Te3 pseudobinary system. It was also proved that thermal stability of β phase is limited—it slowly decomposes below 633 K. In contrast to some reports, it was also indicated that a small amount of Se does not lead to stabilisation of AgSbTe2 crystal structure. Despite slow kinetics of the decomposition processes, thermoelectric properties of the material are notably affected by thermal treatment and amount of Ag2Te precipitations. Maximal ZT value of prepared materials varies from 0.65 at 575 K to 1.07 at 563 K.
Highlights
AgSbTe2 is widely known ternary chalcogenide and it has been a subject of numerous studies due to its promising thermoelectric properties: high Seebeck coefficient above 300 lV KÀ1 and extremely low thermal conductivity in the range of 0.6– 0.7 W mÀ1 KÀ1.1 As a result, some authors report very high thermoelectric figure of merit ZT > 1.4 for samples with various amount of dopant.[2,3,4] AgSbTe2 is used as a component of alloys
We have found that thermal treatment at temperatures above 633 K does not lead to the decomposition of the b phase
We have confirmed that the b phase is the only stable ternary phase in the Sb2Te3-Ag2Te system
Summary
AgSbTe2 is widely known ternary chalcogenide and it has been a subject of numerous studies due to its promising thermoelectric properties: high Seebeck coefficient above 300 lV KÀ1 and extremely low thermal conductivity in the range of 0.6– 0.7 W mÀ1 KÀ1.1 As a result, some authors report very high thermoelectric figure of merit ZT > 1.4 for samples with various amount of dopant.[2,3,4] AgSbTe2 is used as a component of alloys. First experimental results of crystallographic properties of AgSbTe2 were reported by Geller and Wernick.[7] They assumed that single crystals prepared by them had rock salt structure (Fm3m), with Ag and Sb atoms distributed statistically in one of the Wyckoff positions (4a) and Te atoms occupying the second one (4b). Geller and Wernick observed that the nature of the disorder should be complicated because both type of atoms: Ag and Sb differ significantly in electronic structure, atomic radius, and other chemical properties. Others consider different probable superstructures, e.g. tetragonal P4/mmm or trigonal R3m8 to explain unusual electronic properties of this compound
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