Published online by Cambridge University Press: 01 February 2011
Our research on ternary / quaternary chalcogenides for thermoelectric applications has lead to the identification of new interesting compounds and better understanding of the chemistry and physical properties of complex chalcogenides. The chemical, geometric, electronic diversity and flexibility has been well demonstrated in BaBiSe3 and Sr4Bi6Se13 type compounds. This presents both a challenge and more opportunity in controlling and optimizing the thermoelectric properties of these complex chalcogenides, compared with elemental and binary compounds. The importance of multivalley band structure in thermoelectric materials is emphasized. Only compounds with high crystal symmetry have the possibility of having a large number of degenerate valleys in the conduction bands or peaks in the valence bands, respectively. However, most of the complex chalcogenides crystallize in low crystal symmetry. An Edisonian method of exploratory synthesis and characterization may be the working approach to find good thermoelectric materials with ZT higher than 4.