Control of Thermoelectric Properties through the addition of Ag in the Bi0.5Sb1.5Te3Alloy

In this study, the thermoelectric properties of the Ae-doped Bi0.5Sb1.5Te3 compounds were investigated in the temperature ranee from 323 K to 573 K. Ingots were fabricated by a conventional melting process and the powder crushed from ingots was then sintered using a hot-pressing method. The temperature dependence of the Seebeck coefficient and the electrical conductivity of the Ag-doped Bi0.5Sb1.5Te3 compound are characteristic of degenerate semiconductors, which is fairly different from the conventional Bi0.5Sb1.5Te3 compound. The power factor (alpha(2)sigma) of the quaternary compound was larger than that of the ternary, which is mainly due to the increase in the electrical conductivity with doping content of Ag. The thermal conductivity was greater than that of the Ag-freeBi(0.5)Sb(1.5)Te(3)compound in the temperature range from 323 K to 523 K. The lattice thermal conductivity showed low values throughout the temperature range. The maximum value of the dimensionless figure of merit (ZT) of the 0.05 wt. % Ag-doped compound and the ternary alloy were 1.2 at 373 K and 0.88 at 323 K, respectively. Each of the maximum peak ZT shifts to a higher temperature region with increases in the doping content of Ag. This is likely due to the control of the lattice thermal conductivity by the twin structure, which had a nano-ordered layer.