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In this talk I am going to present our very recent discovery of a new thermoelectric material: MgAgSb with ZTs of~0.9 at room temperature and~1.4 at 200℃,and a heat to electricity conversion efficiency of~9%that is much higher than that of bismuth telluride.It is well known that bismuth telluride has been the only thermoelectric material with thermoelectric figure-of-merit(ZT)of slightly above 1 in the temperature range of 20 and 150℃ since its discovery in 1950s.It has been primarily used for cooling even though power generation has also been attempted for hot side of 250℃ and code side of~20℃ for the efficiency of~6%.A material that is better than bismuth telluride in the same temperature is extremely important for both cooling and power generation considering the rareness of tellurium.The materials are made by ball milling powders of elements of Mg,Ag,and Sb in a two-step process and hot pressing the powders into dense bulk samples with grains smaller than 20 nm.The small grain size together with point defects including vacancies and antisites in the structure are the main reasons for the very low thermal conductivity of~0.7 W m-1 K-1 at room temperature.If time allows,I am also going to present another recent discovery of a high ZT material at cryogenic temperature showing a power factor more than 130 W m-1 K-2 that is 3-4 times higher than the best power factor of bismuth telluride.