Enhancing thermoelectric properties of a p-type Mg3Sb2- based Zintl phase compound by Pb substitution in the anionic framework

Abstract

Mg₃Sb₂-based Zintl compounds have recently attracted attention as a potential candidate for thermoelectric applications due to their low thermal conductivity and promising thermoelectric performance (i.e. ZT = 0.6 at 773 K in Mg₃Sb_2−xBi_x). We have reported previously that isoelectronic Bi³⁻ substitution of Sb³⁻ leads to a moderate increase in the electrical conductivity, enhanced Seebeck coefficient and reduced thermal conductivity. Herein, we report a large enhancement of the electrical conductivity while maintaining the Seebeck coefficient by substituting Pb⁴⁻ on Sb³⁻ sites in Mg₃Sb_2−xPb_x (0 ≤ x ≤ 0.3) alloys. Transport measurements reveal that optimum doping of 10 at% Pb⁴⁻ on Sb³⁻ enhances the ZT to 0.84 at 773 K which is comparable to bismuth telluride and selenide industrial materials which are toxic and expensive. The enhancement in ZT is attributed to a decrease in lattice thermal conductivity and simultaneously an increase in the power factor resulting from the significant increase in the electrical conductivity. We observe that Pb⁴⁻ substitutions on Sb³⁻ sites in Mg₃Sb_2−xPb_x (0 ≤ x ≤ 0.3) increase the hole carrier concentration. Electronic transport data of Mg₃Sb_2−xPb_x (0 ≤ x ≤ 0.3) alloys have been analyzed using a single parabolic band model and have been compared to Mg₃Sb₂. The relatively high figure of merit and affordable material ingredients coupled with one step synthesis process makes these materials a promising cost effective solution as thermoelectric materials.