Improvement in thermoelectric properties of Zn-Mn co-doped nanostructured SnTe through band engineering and chemical bond softening

In this work, we used solvothermal technique to synthesize thermoelectrically viable Zn-Mn co-doped SnTe materials. However, the thermoelectric (TE) performance of pure SnTe is subpar due to the significant energy gap between its valence bands, inherent Sn-vacancies, and high electrical thermal conductivity. Band structure engineering and carrier concentration optimization of SnTe following Zn-Mn co-doping have the potential to enhance the Seebeck coefficient. In turn, a boost in the Seebeck coefficient significantly improved the power factor in Sn0.89Mn0.09Zn0.02Te by about five times as compared to pure SnTe at 473 K. The minimum lattice thermal conductivity (kappa L) in Sn0.89Mn0.09Zn0.02Te is 0.54 W m-1K-1 at 473 K, which is almost half that of pure SnTe. The lower lattice thermal conductivity of co-doped samples may be a result of (i) a decrease in phonon group velocity by chemical bond softening and (ii) phonon scattering caused by nanostructuring, point defects, and grain boundaries. Consequently, maximum zT = 0.11 has been achieved in Sn0.89Mn0.09Zn0.02Te at 473 K, which is about five times that of pristine SnTe. Material quality factor (B) of Sn0.89Mn0.09Zn0.02Te is almost triple that of pristine SnTe at 473 K, which implies that Zn-Mn co-doped SnTe is more suited to construct a TE device. An increase in electric transport properties (weighted mobility and electronic quality factor) and a decrease in kappa L after Zn-Mn co-doping contribute to the enhancement of B. The findings of this investigation suggest that the addition of Zn and Mn to SnTe can improve its TE performance.