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.

Energy conversion Energy conversion V 1650Cubic AgPb m SbTe 2+m : Bulk Thermoelectric Materials with High Figure of Merit.-The title materials with m = 10 and 18 are n-type semiconductors exhibiting a high thermoelectric figure of merit of about 2.2 at 800 K. They are expected to outperform all reported bulk thermoelectrics in the temperature range 600-900 K and to find applications in thermoelectric power generation from heat sources, such as vehicle exhaust, coal-burning installations, or electric power utilities. With a hot source of 900 K and a temperature difference of about 500 K, a conversion efficiency of more than 18% may be achieved. -(HSU, K. F.; LOO, S.; GUO, F.; CHEN, W.; DYCK, J. S.; UHER, C.; HOGAN, T.; POLYCHRONIADIS, E. K.; KANATZIDIS*, M. G.;

Most materials expand upon heating. Although rare, some materials expand on cooling, and are said to exhibit negative thermal expansion (NTE); but the property is exhibited in only one crystallographic direction. Such materials include silicon and germanium at very low temperature (<100 K) and, at room temperature, glasses in the titania-silica family, Kevlar, carbon fibres, anisotropic Invar Fe-Ni alloys, ZrW2O3 (ref. 4) and certain molecular networks. NTE materials can be combined with materials demonstrating a positive thermal expansion coefficient to fabricate composites exhibiting an overall zero thermal expansion (ZTE). ZTE materials are useful because they do not undergo thermal shock on rapid heating or cooling. The need for such composites could be avoided if ZTE materials were available in a pure form. Here we show that an electrically conductive intermetallic compound, YbGaGe, can exhibit nearly ZTE--that is, negligible volume change between 100 and 400 K. We suggest that this response is due to a temperature-induced valence transition in the Yb atoms. ZTE materials are desirable to prevent or reduce resulting strain or internal stresses in systems subject to large temperature fluctuations, such as in space applications and thermomechanical actuators.