Enhancing thermoelectric properties of a p-type Mg3Sb2- based Zintl phase compound by Pb substitution in the anionic framework†
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 Mg3Sb2−xBix). 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 Mg3Sb2−xPbx (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 Mg3Sb2−xPbx (0 ≤ x ≤ 0.3) increase the hole carrier concentration. Electronic transport data of Mg3Sb2−xPbx (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.