Sim Loo

The conversion of heat to electricity by thermoelectric devices may play a key role in the future for energy production and utilization. However, in order to meet that role, more efficient thermoelectric materials are needed that are suitable for high-temperature applications. We show that the material system AgPb(m)SbTe(2+m) may be suitable for this purpose. With m = 10 and 18 and doped appropriately, n-type semiconductors can be produced that exhibit a high thermoelectric figure of merit material ZTmax of approximately 2.2 at 800 kelvin. In the temperature range 600 to 900 kelvin, the AgPb(m)SbTe(2+m) material is expected to outperform all reported bulk thermoelectrics, thereby earmarking it as a material system for potential use in efficient thermoelectric power generation from heat sources.

The compound AgBi3S5 (I) (synthetic pavonite) and its solid solution AgSbxBi3-xS5 (x = 0.3) (II) were prepared by direct combination of elemental Ag, Bi, Sb, and S. They crystallize in the monoclinic space group C2/m with a = 13.345(3) Å, b = 4.0416(8) Å, c = 16.439(3) Å, and β = 94.158(3)° for I and a = 13.302(4) Å, b = 4.0381(11) Å, c = 16.388(5) Å, and β = 94.347(5)° for II. The Bridgman technique was used to grow bulk crystals of these materials. The crystal structure refinements, physicochemical properties, and thermoelectric properties of these materials are presented. The thermoelectric power for AgBi3S5 and AgSb0.3Bi2.7S5 showed −64 and −98 μV/K, respectively, with room-temperature electrical conductivity of 489 and 260 S/cm. The thermal conductivity for both compounds at room temperature was measured to be very low at ∼1 W/m·K, respectively. Electronic band structure calculations for AgBi3S5 suggest the importance of silver d-states to the charge transport and also indicate the presence of an indirect energy gap.

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