Atomic-scale insights into the failure origins of polycrystalline thermoelectric materials: CoSb3, Mg2Si, and SnSe

ZS Lei and XX Wang and ZT Lu and XG Huang and WJ Li and XB Feng and G Chen and PC Zhai and B Duan and GD Li and QJ Zhang, ACTA MATERIALIA, 298, 121416 (2025).

DOI: 10.1016/j.actamat.2025.121416

Studying the mechanical properties of polycrystalline thermoelectric materials is crucial for improving device lifespan. In this work, we developed highly accurate potential function models for CoSb3, Mg2Si, and SnSe using a deep learning approach. The newly proposed models demonstrate an ability to accurately predict the elastic parameters, potential energy curves, and potential energy surfaces. Utilizing these novel potential models, we elucidate the origins of failure in these three polycrystalline TE materials from an atomic perspective and propose corresponding enhancement strategies. In polycrystalline CoSb3, the weak coherence of grain boundaries leads to failure originating from the breaking of short Co-Sb bonds at the grain boundaries. In Mg2Si, the grain boundaries consist of densely packed Mg-Si polyhedra with strong coherence, and failure is initiated by the breaking of Mg-Si bonds. In SnSe, the grain boundaries are wide and soft, and during failure, pre- existing or surface-cleaved Sn-Se bond chains can bridge different grains over extended periods. Based on these characteristics, the mechanical performance of CoSb3 and Mg2Si can be enhanced by doping Co and Si atoms at the grain boundaries, respectively. For SnSe, equiaxed grains ensure isotropic stress distribution, which is essential to exploit the deformation accommodation capacity inherent to its low- energy grain boundaries.

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