Enhanced thermoelectric performance of In-doped and AgCuTe-alloyed SnTe through band engineering and endotaxial nanostructures.

Endotaxial nanostructures can reduce lattice thermal conductivity through enhancing phonon scattering without affecting electrical transport, leading to a high thermoelectric performance. On the other hand, band engineering can enhance electrical transport by improving the Seebeck coefficient through valence band convergence and the resonance level. In this paper, the synergistic effect of band engineering and endotaxial nanostructures was implemented in SnTe thermoelectric materials by alloying with AgCuTe and doping with Indium. The positron annihilation lifetime spectra show that the vacancy concentration in SnTe was reduced after alloying with AgCuTe, which led to a decreasing hole concentration and improved carrier mobility. Additionally, the diffusion of Ag in the matrix during the preparation can facilitate valence band convergence. Therefore, the power factor of SnTe is greatly increased to 18 µW cm-1 K-2 at 800 K, which can be further increased to 21.4 µW cm-1 K-2 at 800 K after In doping due to resonance level formation. Meanwhile, Cu2Te endotaxial nanostructures also can be observed in the TEM image after SnTe alloying with AgCuTe. So, the lattice thermal conductivity significantly reduced to 0.93 W m-1 K -1 in In-doped and AgCuTe-alloyed SnTe. Finally, we obtain an enhanced ZT value of 1.14 in Sn1.02In0.01Te-1%AgCuTe at 800 K.

Enhanced Thermoelectric Performance of Mg-Doped AgSbTe2 by Inhibiting the Formation of Ag2Te.

The existence of Ag2Te has always been an obstacle for p-type thermoelectric material AgSbTe2 to improve its thermoelectric performance. In this work, AgSb1-xMgxTe2 samples are synthesized by melting-slow-cooling and then spark plasma sintering (SPS). Through increasing the solubility of Ag2Te in the AgSbTe2 matrix by Mg doping, the formation of Ag2Te is inhibited. Density functional theory calculations confirm more valence bands are involved in electrical transport due to Mg doping. Therefore, the electrical conductivity of AgSb1-xMgxTe2 samples has been greatly improved due to the reduction of Ag2Te with n-type electrical conductivity. Moreover, the downward trend of ZT, which is caused by the structural transition of Ag2Te at about 418 K, disappears. Meanwhile, lattice defects form in the AgSb0.98Mg0.02Te2 sample, and Mg doping improves the configurational entropy change, resulting in a decrease in lattice thermal conductivity over the entire temperature range of measurement. Finally, a high ZT value of 1.31 at 523 K is achieved for the AgSb0.98Mg0.02Te2 sample. This study demonstrates that Mg doping can effectively improve AgSbTe2 thermoelectric performance by inhibiting the formation of the Ag2Te impurity phase.