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

Using 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 to PtSn phase transformation, a periodic superlattice substructure and a unique intermediate structure precede the nucleation and growth of the PtSn phase. At the atomic level, all stages of the transformation are templated by the anisotropic crystal structure of the parent PtSn phase. In the case of the PtSn to PtSn transformation, the anisotropy in the structure of product PtSn 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.