Enhanced fracture toughness of Al and Bi co-doped Mg₂Si by metal nanoparticle decoration

We herein report the effects of metal nanoinclusions (Cu, Al, and Sn) embedded at grain boundaries on the thermoelectric transport and mechanical properties of Mg₂Si-based compounds. Hybrid powders of microscale Al and Bi co-doped Mg₂Si (Mg_1.96Al_0.04Si_0.97Bi_0.03) and nanoscale metal particles were synthesized by a nanometal decoration technique and their nanocomposites were fabricated by a spark plasma sintering process. In compacted polycrystalline bulks, homogeneous dispersion of metal nanoparticles (~150 nm) was readily achieved at grain boundaries. The thermoelectric performance of the nanocomposites deteriorated mainly because of the reduced mobility owing to intensified electron scattering at the phase boundaries between the Mg₂Si matrix and metal nanoinclusions, while the fracture toughness (~1.10 MPa m^1/2, 35% improvement) was significantly enhanced on introducing Al nanoparticles.