Improvement of thermoelectric properties of SnTe by Mn-Bi codoping

SnTe is an attracted lead-free thermoelectric material, but the thermoelectric performance is severely limited by the high hole concentration, undesirable valence band structure and high thermal conductivity. In this work, we study the multiple effects of Mn-Bi codoping in SnTe to synergistically improve the overall power factor and ZT values. It is found that the Mn-Bi codoping effectively reduces the hole concentration to an optimal range. As expected, Mn and Bi doping obviously decreases the energy separation between the two valence band maxima, enabling pronounced band convergence and improved Seebeck coefficient. Moreover, Mn-Bi codoping introduces various phonon scattering centers to scatter a wide spectrum of phonons for a suppressed lattice thermal conductivity of 0.67 W m(-1) K-1 at 850 K. The synergy of these effects yields a peak ZT of 1.3 at 850 K and an average ZT of 0.68 (300-850 K) in Sn0.90Mn0.07Bi0.03Te, suggesting SnTe-based material a promising candidate for medium-temperature thermoelectric applications.