Effects of the Annealing Process and Sb Doping on the Microstructure, Thermoelectric Performance, and Mechanical Processability of <i>β</i> -FeSi ₂

The practical application of eco-friendly <i>β</i>-FeSi₂ thermoelectric materials has been hampered by high thermal conductivity, prolonged synthesis, and inherent brittleness. This study addresses these critical challenges through the synergistic integration of the annealing process and antimony (Sb) doping. We reduced the holding time from the conventional value of more than 48 h to merely 16 h by optimizing the annealing process, while the thermal conductivity is decreased by approximately 51%. Building on this achievement, we synthesized the Fe_0.94Co_0.06Si_2-<i>x</i>Sb_<i>x</i> series and realized the trade-off between the thermoelectric and mechanical properties. Specifically, Fe_0.94Co_0.06Si_1.99Sb_0.01 attains a low thermal conductivity of 3.53 W m^-1 K^-1 at 873 K, which is 18.2% lower than that of the Fe_0.94Co_0.06Si₂ sample. Simultaneously, Sb doping dramatically reduces the Young's modulus, shear modulus, and Vickers hardness, thereby markedly improving machinability, while the thermoelectric figure of merit value is stably maintained at around 0.15. This outcome fully validates the effectiveness of the synergistic integration of the annealing process and Sb doping in maintaining favorable thermoelectric performance while significantly enhancing mechanical processability.