Effect of non-stoichiometry on thermoelectric properties of gamma-Tb2S(3-x)

The electrical resistivity, thermopower, and thermal conductivity measurements have been made on the cubic gamma-Tb2S(3-x) with low sulfur content. The powders were synthesized by reacting the oxide with carbon disulfide at 1323 K, followed by heating at 1853 K. The heat treatments lead to a decrease in the sulfur content. In order to obtain the samples close to the theoretical density solids, the powders were consolidated by a pulse electric current sintering at 1673 K. In the temperature range from 300 to 1000 K, all the samples exhibit a high negative thermopower. The electrical resistivity and the magnitude of thermopower increase almost linearly with increasing temperature. The thermal conductivity ranges from 1.3 to 1.4 W/Km. The thermoelectric properties improve for decreasing sulfur content. A maximum thermoelectric figure of merit of 0.17 was obtained at 873 K for these compounds.