LAUSR

Abstract P-type polycrystalline Sn1-vS compounds and Sn0.985S1-xSex solid solutions are prepared by combining mechanical alloying (MA) and spark plasma sintering (SPS). Dislocations in the grains are successfully introduced through vacancy engineering in Sn1-vS compounds. Point defects provide high–frequency phonons scattering from the Se substitution in Sn0.985S1-xSex, in addition to the strong scattering of mid–frequency phonons by dislocations. This leads to a low lattice thermal conductivity and an enhanced thermoelectric figure of merit (ZT) of ≈1.1 for the Sn0.985S0.25Se0.75 at 823 K. The Ag dopant is selected to further enhance the electrical transport properties of the optimized composition. The power factor improved from 4.5 (Sn0.985S0.25Se0.75) to ≈5.3 μW m−1 K−2 for Sn0.978Ag0.007S0.25Se0.75 sample. Surprisingly, the Ag doping induced a nanostructured matrix with dispersed spherical coherent precipitates of AgSnSe2 inside the grains, which further strengthens the scattering of phonons. The presence of AgSnSe2 nanoscale precipitates inside the grains and dislocations–induced by Ag at the grain boundaries contributes to an impressively low lattice thermal conductivity (κL). Consequently, the maximum ZT ≈1.75 at 823 K is achieved for the Sn0.978Ag0.007S0.25Se0.75 sample.