Synergistic effects of Ag-Bi co-doping on thermoelectric properties of Mg2Si0.3Sn0.7 solid solutions

Mg 2 Si 1-x Sn x solid solutions are promising thermoelectric materials due to the inexpensive and abundant nature of their components, their environmental friendliness and their flexibility in terms of optimising their thermoelectric properties. In this study, we report on the thermoelectric properties enhancement of n-type Mg 2 Si 0.3 Sn 0.7 solid solutions doped with aliovalent elements, donor (Bi) and acceptor (Ag), respectively. Samples were synthesized via conventional melting followed by spark plasma sintering. Co-doping led to carrier concentration and mobility tuning, resulting in a significantly increased Seebeck coefficient while maintaining high electrical conductivity. Consequently, the power factor reached 44.67 × 10 −3 W·m - ¹ ·K −2 at 650 K for Mg 1.98 Ag 0.02 Si 0.29 Sn 0.69 Bi 0.02 . Furthermore, lattice thermal conductivity was reduced via enhanced phonon scattering caused by point defects and suppressed bipolar conductivity attributed to a widened band gap and increased carrier density. The combined effects yielded improved ZT values, peaking at 1.12 at 674 K and 1.13 at 721 K for Mg 1.99 Ag 0.01 Si 0.29 Sn 0.69 Bi 0.02 and Mg 1.98 Ag 0.02 Si 0.29 Sn 0.69 Bi 0.02 , respectively. These results highlight the potential of Ag–Bi co-doping as a robust strategy to enhance the thermoelectric efficiency of Mg 2 Si 1-x Sn x based materials.