Nanodopant Induced Band Modulations and Electronic Transport Properties in AgPb$_m$SbTe$_{2+m}$-type Thermoelectric Nanocomposites*

The remarkable performance of many novel thermoelectric materials is attributed to their nanosized inclusions. By extensive first-principles calculations we show the distinct band structure modulation in AgPb$_m$SbTe$_{2+m}$ (LAST)-type nanocomposites. A band gap widening and conduction band minimum splitting process resulting from the nanodopants is discovered for a series of nanocomposites. Boltzmann transport calculations demonstrate that this process leads to a pronounced change in the high temperature electronic transport. The effects of different substitutional elements and atomistic orderings are discussed. Our results provide new understanding of nanosized doping in thermoelectric materials and narrow gap semiconductors.