Effect of Ce Substitution for Sb on the Thermoelectric Properties of AgSbTe2 Compound

We have prepared Ce-doped polycrystalline AgSbTe2.01 compounds from high-purity elements by a melt-quench technique followed by spark plasma sintering, and their thermoelectric transport properties have been investigated in the temperature range of 300 K to 625 K. The actual concentration of Ce was much less than the initial composition, but roughly proportional to it. Small additions of Ce shifted the composition of the homogeneity range from the nearly ideal atomic ratio Ag:Sb:Te = 0.98:1.02:2.01 toward Sb rich (Ag poor), and led to the reemergence of Ag2Te impurity in AgSbTe2 compound. The Ce-doped samples possessed lower electrical conductivity compared with the undoped AgSbTe2.01 compound at room temperature, but the carrier mobility and effective mass were essentially constant, indicating intact band structure near the covalent band maximum upon Ce substitution for Sb. Due to the decrease of lattice vibration anharmonicity resulting from Ce substitution for Sb, the lattice conductivity of the Ce-doped samples was about 0.1 W m−1 K−1 higher than that of the AgSbTe2.01 sample, and the magnitude spanned the range from 0.30 W m−1 K−1 to 0.55 W m−1 K−1. A ZT of 1.20 was achieved at about 615 K for the AgSb0.99Ce0.01Te2.01 sample.