Tellurium Doping-Driven Material and Device Performance of Mg3(Sb0.3Bi0.7)2-Based Alloys

Mg3(Sb,Bi)2-based alloys have attracted considerable attention as promising n-type thermoelectric materials for low- to mid-temperature waste heat recovery. While recent studies have reported a broad thermoelectric performance window in these materials, the Te-doped compositions remain underexplored in terms of device-level performance. Here, we investigate Mg3(Sb0.3Bi0.7)2-xTex with x = 0.007 and 0.03, representing two distinct donor doping regimes, and systematically correlate their thermoelectric transport properties with single-leg device performance. The lightly doped composition (x = 0.007) exhibits a higher Seebeck coefficient and reaches a peak ZT of ∼0.87 at 468 K. In contrast, the heavily doped composition (x = 0.03) shows higher electrical conductivity and achieves a higher peak ZT of ∼0.96 at 590 K. Despite lower peak ZT, the single-leg device of lightly doped composition delivers a little higher device efficiency (η) of ∼7%, compared to ∼6.6% for the heavily doped leg at ΔT ≈ 267 K. This is due to higher average temperature-dependent transport properties of x = 0.007 in operating ΔT, as confirmed by the cumulative temperature dependency (CTD) model. These results establish a device-oriented, composition-specific optimization strategy for Mg3(Sb,Bi)2-based thermoelectrics and highlight the importance of efficiency-driven design for practical energy harvesting applications.