Attaining High Figure of Merit in the N-Type Bi₂Te_2.7Se_0.3-Ag₂Te Composite System via Comprehensive Regulation of Its...

n-Type Bi₂Te_2.7Se_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 Ag₂Te 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 Ag₂Te nanophase. Consequently, the largest ZT_max = 1.31 (at 350 K) and average ZT_ave = 1.16 (300-500 K) are achieved for the Bi₂Te_2.7Se_0.3-0.3 wt % Ag₂Te composite sample, leading to a projected conversion efficiency η = 8.3% (300-500 K). The present results demonstrate that incorporation of nanophase Ag₂Te is an effective approach to boosting the thermoelectric performance of BTS.