Microstructure and thermoelectric properties of as-cast Ag2Te/AgBiTe2 and Ag2Te/Bi2Te3 two-phase alloys

Abstract

The microstructure and thermoelectric properties of Ag2Te/AgBiTe2/Bi2Te3 eutectic alloys in the Ag-Bi-Te system were investigated in the present study. A self-consistent, thermodynamically optimized database of the Ag-Bi-Te system was developed to explain the microstructural features in the investigated alloys. Samples namely B0 (Bi2Te3 – 0 at.% Ag), B1 (Bi2Te3 – 5 at.% Ag), B2 (Bi2Te3 – 18.35 at.% Ag), B3 (Bi2Te3 – 28.35 at.% Ag), and B4 (Bi2Te3 – 38.35 at.% Ag) were synthesized by flame melting. Scanning electron micrographs of alloys reveal lamellar eutectic structures in which alloys B1 and B2 exhibit two distinct phases, consisting of β-Bi2Te3 and AgBiTe2, whereas alloys B3 and B4 display phase compositions corresponding to Ag2Te and AgBiTe2 phases. The X-ray diffraction reveals that the solidified alloys have hexagonal (AgBiTe2, Bi2Te3) and cubic β-Ag2Te crystal structures. The Scheil cooling calculations of these alloys using the developed thermodynamic database explain the microstructural features of the alloys. Furthermore, the mechanical characteristics of eutectic alloys B1 and B3 demonstrated improved hardness values, measuring 1.1 GPa and 1.2 GPa, respectively. Moreover, the transport characteristics show favourable attributes for thermoelectrics in high-temperature applications. It is important to highlight that all these alloys showcase transport properties that are highly advantageous for thermoelectrics. Notably, alloy B2 distinguishes itself with a remarkable ZT value of 0.42 at 540 K.