Attaining High Figure of Merit in the N-Type Bi 2 Te 2.7 Se 0.3 -Ag 2 Te Composite System via Comprehensive Regulation of Its Thermoelectric Properties.

n-Type Bi 2 Te 2.7 Se 0.3 (BTS) is the state-of-the-art thermoelectric material near room temperature. However, the figure of merit ZT of commercial BTS ingots is still limited and further improvement is imperative for their wide applications. Here, the results show that through dispersion of the Ag 2 Te nanophase in BTS, one can not only elevate its power factor (PF) by as high as 14% (at 300 K) but also reduce its thermal conductivity κ tot to as small as ∼29% (at 300 K). Experimental evidences show that the improved PF comes from both increased electron mobility via inhibited Te vacancies and enhanced thermopower due to energy filtering effect, while the reduction of κ tot originates from the drop of both electronic thermal conductivity largely owing to the reduced number of vacancy V Te ·· and intensified phonon scattering chiefly from the dispersed Ag 2 Te nanophase. Consequently, the largest ZT max = 1.31 (at 350 K) and average ZT ave = 1.16 (300-500 K) are achieved for the Bi 2 Te 2.7 Se 0.3 -0.3 wt % Ag 2 Te composite sample, leading to a projected conversion efficiency η = 8.3% (300-500 K). The present results demonstrate that incorporation of nanophase Ag 2 Te is an effective approach to boosting the thermoelectric performance of BTS.