Microstructure analyses and thermoelectric properties of Ag1−xPb18Sb1+yTe20

► SEM and TEM microstructure investigation of long-term annealed AgPb18SbTe20. ► SEM and thermoelectric studies on Ag1−xPb18Sb1+yTe20. ► Discussion concerning structure-property relationship in long-term annealed AgPb18SbTe20. ► Correlation between Ag1−xPb18Sb1+yTe20 microscale structure and electronic properties.