Electronic structure of AgPb _mSbTe _m+2 compounds - Implications on thermoelectric properties

Novel quaternary compounds AgPb _mSbTe _m+2 (LAST-m) with different m values have been synthesized recently and some of these compounds show promising thermoelectric properties at high temperatures. The two end members of the series, PbTe (m=∞) and AgSbTe ₂ (m=0), are also known to be good thermoelectrics. In this paper, we discuss the results of ab initio electronic structure calculations for these two end members and for LAST-2 and LAST-14 to see how the electronic structure near the chemical potential μ, evolves with m. Whereas PbTe and LAST-14 are narrow band gap semiconductors, the other two compounds show pseudo-gap structure. Even in the absence of a true gap, the rapidly varying density of states (DOS) near μ may be conducive to large Seebeck coefficient in LAST-2, LAST-14, and AgSbTe ₂.