Microstructure analyses and thermoelectric properties of Ag{sub 1-x}Pb{sub 18}Sb{sub 1+y}Te{sub 20}

This study reports microstructural investigations of long-term annealed Ag{sub 1-x}Pb{sub m}Sb{sub 1+y}Te{sub 2+m} (m=18, x=y=0, hereinafter referred to as AgPb{sub 18}SbTe{sub 20}) (Lead-Antimony-Silver-Tellurium, LAST-18) as well as of Ag{sub 1-x}Pb{sub 18}Sb{sub 1+y}Te{sub 20}, i.e. Ag-deficient and Sb-excess LAST-18 (x{ne}0,y{ne}0), respectively. Two different length scales are explored. The micrometer scale was evaluated by SEM to analyze the volume fraction and the number of secondary phases as well as the impact of processing parameters on the homogeneity of bulk samples. For AgPb{sub 18}SbTe{sub 20}, site-specific FIB liftout of TEM lamellae from thermoelectrically characterized samples was accomplished to investigate the structure on the nanometer scale. High-resolution TEM and energy-filtered TEM were performed to reveal shape and size distribution of nanoprecipitates, respectively. A hypothesis concerning the structure-property relationship is set out within the frame of a gradient annealing experiment. This study is completed by results dealing with inhomogeneities on the micrometer scale of Ag{sub 1-x}Pb{sub 18}Sb{sub 1+y}Te{sub 20} and its electronic properties. Highlights: Black-Right-Pointing-Pointer SEM and TEM microstructure investigation of long-term annealed AgPb{sub 18}SbTe{sub 20}. Black-Right-Pointing-Pointer SEM and thermoelectric studies on Ag{sub 1-x}Pb{sub 18}Sb{sub 1+y}Te{sub 20}. Black-Right-Pointing-Pointer Discussion concerning structure-property relationship in long-term annealed AgPb{sub 18}SbTe{sub 20}. Black-Right-Pointing-Pointer Correlation between Ag{sub 1-x}Pb{sub 18}Sb{sub 1+y}Te{sub 20} microscale structure and electronic properties.