Constructing Coated Grain Nanocomposites and Intracrystalline Precipitates to Simultaneously Improve the Thermoelectric and Mechanical Properties of SnTe by MgB₂ and Sb Co‐Doping

Abstract Thermoelectric materials should be highly efficient and mechanically robust to satisfy the requirements of engineering applications. Herein, an integrated optimization strategy to improve both the thermoelectric performance and mechanical strength of SnTe is proposed. First, grain boundary engineering is applied to SnTe via MgB₂ doping. The decomposition of MgB₂ results in the Mg‐substituted SnTe solid solution and a special “core–shell” structure of Mg‐B compounds coated SnTe grain remarkably reducing the lattice thermal conductivity. Subsequently, trivalent Sb atoms are introduced to tune the carrier concentration and optimize the electrical performance of the MgB₂‐doped sample. Sb‐rich Sn‐Te precipitates inside the grains further diminish the lattice's thermal conductivity. Consequently, a prominent improvement in average ZT of ≈117% is achieved for Sn_0.78Sb_0.16Te(MgB₂)_0.09 compared to pristine Sn_1.03Te. Moreover, the compressive yield strength and Vickers hardness of Sn_0.78Sb_0.16Te(MgB₂)_0.09 are significantly increased by ≈168% and 176% relative to pristine Sn_1.03Te, respectively. The quantitative strengthening models including grain boundary, dislocation, solid solution, intergranular, and precipitation strengthening in MgB₂‐ and MgB₂‐Sb‐doped Sn_1.03Te samples are proposed, showing that the dominant strengthening mechanism is precipitation strengthening. This work provides an avenue for designing efficient and robust thermoelectric materials toward commercial application.