Carrier–phonon decoupling-driven enhanced thermoelectric performance of Sb–Bi co-doped Mg2Si0.6Sn0.4 solid solution

Strong carrier–phonon coupling poses a significant challenge to decoupling of electrical and thermal transport in Mg2(Si, Sn)-based systems, which limits their thermoelectric performance over a wide temperature range. Herein, we demonstrate that Sb–Bi co-doping in Mg2Si0.6Sn0.4 solid solutions modulates carrier–phonon interactions through acoustic phonon scattering and alloying-induced band structure tuning, respectively. This strategy effectively optimizes the carrier concentration while simultaneously tuning the alloy scattering parameter and acoustic phonon scattering potential, resulting in weakened carrier–phonon coupling and enhanced carrier transport. The optimized composition, Mg2(Si0.6Sn0.4)0.98Bi0.015Sb0.005, exhibits enhanced electrical transport with a high weighted mobility (μW) of 123 cm2 V−1 s−1 and a superior power factor of 3 mW m−1 K−2. Furthermore, the synergistic effect of multiple phonon scattering mechanisms results in an ultra-low lattice thermal conductivity of 0.89 W m−1 K−1. Consequently, a record-high figure of merit (zTmax) of 1.57 at 753 K and  zTavg of ∼0.9 over 303–753 K were achieved, highlighting a promising strategy for optimizing carrier–phonon dynamics in n-type Mg2(Si, Sn)-based thermoelectric (TE) materials.