Mechanical alloying boosted SnTe thermoelectrics

Abstract

The well converged transporting valence bands in SnTe-MnTe alloys ensures a superior electronic performance, while their thermal transport properties still need to be further optimized for higher thermoelectric performance. Herein, the mechanical alloying is utilized to fabricate the SnTe-15%MnTe-2%Bi alloys, leading to a remarkable reduction of grain size as well as the formation of dense dislocations. Unexpectedly, the solubility of MnTe is reduced to ∼6% by mechanical alloying at room temperature, inducing an enhanced phonon scattering from nanoprecipitates. These full-scale hierarchical microstructures effectively decrease the lattice thermal conductivity of SnTe-15%MnTe-2%Bi to ∼0.5 W m−1 K−1 at 850 K. In addition, the increased vacancy formation energy triggers a reduction in carrier concentration (∼3 × 1019 cm−3) due to the decreased MnTe content in matrix. Moreover, the energy filtering effect through precipitate-matrix interface enables an improvement in Seebeck coefficient. Accordingly, the figure of merit of SnTe-15%MnTe-2%Bi is dramatically increased to ∼1.5 at 850 K by mechanical alloying. This work clearly demonstrates that mechanical alloying changes the composition and microstructure of materials, which significantly affect the thermoelectric transport properties, enabling an obvious performance enhancement.