Phase compositions, nanoscale microstructures and thermoelectric properties in Ag2−ySbyTe1+y alloys with precipitated Sb2Te3 plates

Nonstoichiometric ternary thermoelectric materials Ag2−ySbyTe1+y (y = 1.26, 1.29, 1.32, 1.35, and 1.38) were prepared by a direct melt-quench and hot press process. In situ composites of AgSbTe2 and Sb2Te3 were obtained over the entire composition range with a typical Widmanstätten pattern. Thermoelectric properties were measured from 300 K to 673 K, which changed systematically with Sb2Te3 ratio. The phase transition occurring at about 633 K, forming the single phased AgSbTe2, can significantly influence the electrical transport properties. Various crystallographic defects in different scales, such as atomic ordering, nanodomains, dislocations and stacking faults, have been observed by high-resolution transmission electron microscopy and their influences on lattice thermal conductivity have been discussed. Due to the extremely low thermal conductivity (about 0.6 W m−1 K−1) and large positive Seebeck coefficient of ∼250 μV K−1 detected in Ag0.71Sb1.29Te2.29, the maximum dimensionless figure of merit ZT of 1.37 was obtained at 600 K.