Doping effect on thermoelectric properties of nonstoichiometric AgSbTe_2 compounds
Nonstoichiometric ternary thermoelectric materials Ag0.84Sb1.15M0.01Te2.16 (M=Ce, Yb, Cu) were prepared by a direct melt-quench and hot press process. The carrier concentration of all the samples increased after doping. Thermoelectric properties, namely electrical con-ductivity, Seebeck coefficient, and thermal conductivity, were measured from 300 to 673 K. The phase transition occurring at about 418 K representing the phase transition from b-Ag2Te to a-Ag2Te influenced the electrical transport properties. The electrical conductivities of Ce and Yb doped samples increased after doping from 1.9×104 to 2.5×104 and 2.3×104 S·m-1, respectively, at 673 K. Also, at room temperature, the Seebeck coefficient of the Ce doped sample relatively increased corresponding to the high carrier concentration due to the changes in the band structure. However, all the thermal conductivities increased after doping at low temperature. Because of the higher thermal conductivity, the dimensionless figure of merit ZT of these doped samples has not been improved.