Structural Anisotropy-Driven Atomic Mechanisms of Phase Transformations in the Pt-Sn System.

Using in situ atomic-resolution scanning transmission electron microscopy, atomic movements and rearrangements associated with diffusive solid to solid phase transformations in the Pt-Sn system are captured to reveal details of the underlying atomistic mechanisms that drive these transformations. In the PtSn ₄ to PtSn ₂ phase transformation, a periodic superlattice substructure and a unique intermediate structure precede the nucleation and growth of the PtSn ₂ phase. At the atomic level, all stages of the transformation are templated by the anisotropic crystal structure of the parent PtSn ₄ phase. In the case of the PtSn ₂ to Pt ₂ Sn ₃ transformation, the anisotropy in the structure of product Pt ₂ Sn ₃ dictates the path of transformation. Analysis of atomic configurations at the transformation front elucidates the diffusion pathways and lattice distortions required for these phase transformations. Comparison of multiple Pt-Sn phase transformations reveals the structural parameters governing solid to solid phase transformations in this technologically interesting intermetallic system.