Decoupling Electrical and Thermal Transport in p-Type Mg ₂ ZnSb ₂ through a Binary Dopant Synergistic Strategy for High Thermoelectric Performance

Mg-based Zintl-phase thermoelectrics are competitive candidates for commercial applications, but the performance of p-type Mg-based AB₂X₂ Zintl materials still lags behind that of their n-type counterparts. Here, we demonstrate that Li-IV (IV = Si, Ge, Sn) dual doping in the Mg₂ZnSb₂ lattice effectively decouples the optimization of the electronic and thermal transport properties. With Mg_2.06Zn_1-xLi_xSb_2-yGe_y as an illustration, within a certain total dopant content, the electrical transport properties show little sensitivity to the Li:Ge ratio, while the thermal conductivity can be significantly modulated. Specifically, the samples dual-doped with Li and Ge exhibit carrier concentration behavior and valence band structure similar to those doped with Li alone, whereas their thermal conductivity is dramatically reduced due to Ge introduction. Furthermore, the codoping strategy restrains the bipolar effect in samples doped solely with Ge at intermediate temperatures by increasing the carrier concentration. By combining a relatively low thermal conductivity with a power factor comparable to that of the Li-doped samples, an optimized composition of Mg_2.06Zn_1.995Li_0.005Sb_1.975Ge_0.025 achieves a peak dimensionless figure of merit (ZT) of 1.14 at 625 K. This work provides an effective approach to selectively reduce thermal conductivity while preserving favorable electrical conductivity and Seebeck coefficient.