Modulating the valence of In on the thermoelectric properties of Pb0.99In0.01Te1-xSx compounds

Abstract

In dopant demonstrates a distinct role in PbTe and PbS compounds though they possess the same crystal structure. Therefore, to unravel how the thermoelectric performance evolves in the In-doped PbTe1-xSx solid solution is crucial. Herein, a series of Pb0.99In0.01Te1-xSx samples were synthesized by conventional melting methods. It is found that doping In in PbTe introduces a shallow level impurity state In3+ and a deep level associated with the In+ state simultaneously. Alloying PbS in Pb0.99In0.01Te1-xSx compounds modulates the valence of In dopant, increasing the relative ratio of In3+ content due to the stronger oxidation capacity of S in comparison with that of Te. This augments the room temperature carrier concentration from 3.03 × 1018 cm−3 for Pb0.99In0.01Te compound to 5.76 × 1018 cm−3 for Pb0.99In0.01Te0.91S0.09 compound. Therefore, an improved power factor of 17.4 μW cm−1 K−2 for Pb0.99In0.01Te0.91S0.09 compound is obtained at room temperature. Additionally, alloying PbS in Pb0.99In0.01Te1-xSx compounds enhances the point defect phonon scattering and lowers the lattice thermal conductivity from 1.83 W m−1 K−1 for Pb0.99In0.01Te compound to 0.74 W m−1 K−1 for Pb0.99In0.01Te0.88S0.12 compound at room temperature. As a consequence, a maximum ZT value of 1.12 at 723 K is attained for Pb0.99In0.01Te0.95S0.05 compound, which is improved by 19% in comparison with that of Pb0.99In0.01Te compound. This work provides a new path for modulating the doping behavior of cation site dopant via alloying on anion site to further improve the ZT value in thermoelectric materials.