Synergistic optimization of thermoelectric properties in Ca(Yb)Mg₂Bi₂ composited SnTe based alloy

SnTe exhibits inferior thermoelectric performance because of the excess Sn vacancies, large energy offset between the two valence bands, and relatively high lattice thermal conductivity. Therefore, it is necessary to adopt a variety of means to optimize its thermoelectric performance synergistically. Here, the microstructure and thermoelectric properties for Sn_0·99In_0·01Te composited with CaMg₂Bi₂ and YbMg₂Bi₂ are reported. Ca (Yb) and Mg doping decreases the energy offset between the two valence bands, leading to an improved Seebeck coefficient. In addition, Bi and Sn phases gradually precipitate with the increase of alloying amount. The large number of phase interfaces and point defects scatter phonons strongly. Meanwhile, Mg volatilization produces lots of pores at grain boundaries, which play an important role in extending the phonon transmission path. These multiple effects lead to an ultralow lattice thermal conductivity. Consequently, peak ZT of 0.94 and 1.14 at 823 K are attained in Sn_0·99In_0·01Te-(CaMg₂Bi₂)_0.025 and Sn_0·99In_0·01Te-(YbMg₂Bi₂)_0.03, corresponding to average ZT (300–823 K) of 0.67 and 0.77, respectively. This work provides an ingenious way to realize extraordinary thermoelectric performance in SnTe.