Phase separation and thermoelectric properties of the Pb0.25Sn0.25Ge0.5Te compound

► Quasi-ternary (Pb,Sn,Ge)Te compounds with Sn (>7 at%) content are single phased at elevated (>600 °C) temperature. ► On cooling, the compounds undergo a discontinuous precipitation process. ► The discontinuous precipitation gives rise to heterogeneously nucleated coupled Pb- and Ge-rich telluride lamellae. ► After aging (>500 h at 400 °C), the microstructure consists of a Pb-rich matrix with spheroidized Ge-rich telluride precipitates. ► The aged compounds display a stable thermoelectric figure of merit, ZT = 0.95.