Improvement of Thermoelectric Properties through Controlling the Carrier Concentration of AgPb18SbTe20 Alloys by Sb Addition

The effect of Sb addition on the thermoelectric properties of the AgPb18Sb1+xTe20 (x = 0 - 1) compounds (LAST-18 compounds) has been investigated in a temperature range between 323 K and 723 K. The measured thermoelectric properties were compared with LAST-18 (x = 0 composition) previously reported and fabricated using the same procedure. All samples showed a negative Seebeck coefficient, which implies the major carrier is the electrons. The carrier concentration of the samples with additional Sb was larger than that of the LAST-18 compounds, indicating that Sb is acting as a donor element in the LAST compounds. From the results of XRD, the Seebeck coefficient, and Hall measurement, the solubility limit of Sb in LAST was estimated. The maximum dimensionless figure of merit, ZT, was obtained for the x = 0.2 composition, where the value was ZT = 1.33 at 723 K. The enhancement of ZT was attributed to the increment of the carrier concentration, resulting in a dramatic reduction of electrical resistivity compared with LAST-18.