Enhanced Thermoelectric Performance of p-Type Mg_3-ZnSb₂/Sb Composites: The Role of ZnSb/Sb Composites

Mg₃Sb₂-based Zintl compounds have garnered recent attention as promising materials for thermoelectric applications due to their low thermal conductivity and high zT values as n-type materials. However, the zT values of p-type materials are lower compared to their n-type counterparts. Through a straightforward process involving cold pressing and evacuating-and-encapsulating sintering, we have successfully synthesized a variety of p-type Mg_3-ZnSb₂/Sb composites by adding the ZnSb-4%Sb composite into the Mg₃Sb₂ host material. Structural analyses have provided insights into the role of the ZnSb-4%Sb composite, demonstrating its significance in Zn doping on the Mg sites and Sb acting as an additive in the composite. The introduction of Zn on the Mg tetrahedral sites enhances the concentration of carriers, while the presence of highly conductive Sb grains facilitates the movement of charge carriers between adjacent Mg_3-ZnSb₂ grains, thereby promoting mobility. Consequently, the electrical resistivity of the Mg_3-ZnSb₂/Sb composites decreases as the Zn content increases. At 710 K, the Mg_1.91Zn_1.09Sb₂/Sb composite exhibits the lowest resistivity, measuring 5.1 mΩ-cm, which is 46 times lower than that of the Mg₃Sb₂ host. Furthermore, the zT value of the Mg_3-ZnSb₂/Sb composites increases with higher Zn content (x), benefiting from a combination of an improved power factor and reduced thermal conductivity. Significantly, our straightforward fabrication process enables us to achieve a maximum zT value of 0.58 at 710 K for the Mg_1.91Zn_1.09Sb₂/Sb composite. This achievement can primarily be attributed to the 8-fold enhancement in power factor compared to the Mg₃Sb₂ host.