Competing Grain Growth Pathways in Anisotropic Bi ₂ Te ₃ ‐Based Thermoelectric Nanoplates

Thermoelectric nanoplates derived from anisotropic van der Waals (vdW) materials such as Bi₂Te₃ are pivotal for flexible electronics and microscale thermal management. Their performance critically depends on grain boundary (GB) microstructure, but the atomic-scale mechanisms governing grain growth in these highly anisotropic systems remain elusive. This particularly concerns the competition between individual nanoplate reshaping driven by facet stabilization and collective merging at GBs. Integrating in situ scanning transmission electron microscopy (STEM), density functional theory (DFT), and molecular dynamics (MD) simulations, these competing pathways in pure Bi₂Te₃ (BT) and Sb-doped (BST) systems are unraveled. Undoped BT nanoplates preferentially undergo atomically localized reshaping, with atoms migrating from high-energy edges to stabilize low-energy facets. Conversely, Sb doping introduces Sb-Te interfacial phases that thermodynamically favor GB coalescence, thereby shifting the dominant pathway to collective merging. This work reveals how chemical modification steers GB evolution, determining whether reshaping or merging predominates. Such understanding is crucial for rationally designing anisotropic layered materials for applications in flexible electronics, topological materials, and energy-efficient devices.