Analysis of Nanostructuring in High Figure-of-Merit Ag1-xPbmSbTe2+m Thermoelectric Materials

• Published in: Advanced functional materials 2009-04, Vol.19 (8), p.1254-1259
• Main Authors: Cook, Bruce A., Kramer, Matthew J., Harringa, Joel L., Han, Mi-Kyung, Chung, Duck-Young, Kanatzidis, Mercouri G.
• Format: Article
• Language: English
• Subjects: nanostructuring; thermoelectric materials; transmission electron microscopy
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.200801284

Thermoelectric materials based on quaternary compounds Ag1−xPbmSbTe2+m exhibit high dimensionless figure‐of‐merit values, ranging from 1.5 to 1.7 at 700 K. The primary factor contributing to the high figure of merit is a low lattice thermal conductivity, achieved through nanostructuring during melt solidification. As a consequence of nucleation and growth of a second phase, coherent nanoscale inclusions form throughout the material, which are believed to result in scattering of acoustic phonons while causing only minimal scattering of charge carriers. Here, characterization of the nanosized inclusions in Ag0.53Pb18Sb1.2Te20 that shows a strong tendency for crystallographic orientation along the {001} planes, with a high degree of lattice strain at the interface, consistent with a coherent interfacial boundary is reported. The inclusions are enriched in Ag relative to the matrix, and seem to adopt a cubic, 96 atom per unit cell Ag2Te phase based on the Ti2Ni type structure. In‐situ high‐temperature synchrotron radiation diffraction studies indicated that the inclusions remain thermally stable to at least 800 K. The nanostructuring occurring in the AgPb18SbTe20 system is documented and it is shown to contain coherent or semi‐coherent Ag‐rich nano‐inclusions, most in range of 2 to 30 nm embedded in an essentially PbTe matrix. The analysis of the nanostructuring supports the mechanism believed to be responsible for achieving a high thermoelectric figure‐of‐merit.