Thermoelectric properties of Mn, Bi, and Sb co-doped SnTe with a low lattice thermal conductivity

Over a period, there has been extensive research on both single and binary elements co-doping in SnTe. For the first time, we have investigated the effects of ternary dopants, Mn, Bi, and Sb, in SnTe with an aim of employing their synergetic effects to improve the Seebeck coefficient, consequently to increase the power factor and to lower the lattice thermal conductivity (κ_lat). Pristine SnTe exhibits a high electrical conductivity of 6320 S/cm, where after Mn isovalent and Bi and Sb aliovalent substitution at the Sn site, the electrical conductivity reduced up to 1530 S/cm at room temperature. As a result of the tuning of the carrier concentration, an increased Seebeck coefficient in all samples is observed. Compared to equivalent doping proportion of each dopant, a higher power factor of ∼22 μW/cmK² is recorded. Stronger phonon scattering resulting from mass fluctuation in the multiple dopants, grain size, embedded nanostructures in the grain, and strained Mn–rich nano–precipitates in the grain boundary results in a low lattice thermal conductivity, with the lowest value recorded being ∼0.86 W/mK at 773 K. As a result, a ZT value of ∼1 at 773 K is recorded for the Sn_0.85Mn_0.09Sb_0.035Bi_0.025Te sample, which is a 271% improvement from our pristine SnTe.