Improved thermoelectric figure of merit of self-doped Ag8-xGeTe6 compounds with glass-like thermal conductivity

Nonstoichiometric Ag8-xGeTe6 (x = 0, 0.01, 0.02, 0.04) compounds with complex crystal structure are demonstrated to exhibit very low thermal conductivities of <0.28 W/m K, comparable with the calculated theoretical minimum thermal conductivity kappa(min). Ag deficiency leads to the improved electrical properties and a maximum thermoelectric figure of merit ZT of 0.85 has been obtained at 623 K for Ag7.99GeTe6, about 30% increase compared to that of stoichiometric Ag8GeTe6. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.