Dislocation-Induced Stop-and-Go Kinetics of Interfacial Transformations

Engineering materials are typically based on multiphase microstructures produced either through the control of phase equilibria or by the fabrication of different materials as in thin-film processing. In both processes, the microstructure relaxes toward equilibrium by mismatch dislocations (or geometric misfit dislocations) across the heterophase interfaces. Fundamental understanding of mismatch dislocations and their dynamic coupling to phase transformations has been a longstanding topic of study. Unfortunately, directly probing misfit dislocation dynamics has been a major challenge due to their buried nature and the difficulty of direct experimental measurements at the atomic scale. Transmission electron microscopy (TEM) is one of the few tools capable of accessing buried interfaces and has demonstrated its versatility and atomic-scale precision in elucidating the location and configuration of misfit dislocations. However, directly probing the dynamic action of mismatch dislocations during phase transformations is challenging because it requires not only a capability to atomically capture the fast evolution of interfaces but also to apply stimuli to drive the interface transformation. Using the example of Cu₂O→Cu interfacial transformation, we demonstrate the unique role of mismatch dislocations in modulating oxide/metal interfacial transformations in an intermittent manner, by which the lateral flow of interfacial ledges is pinned at the core of mismatch dislocations until the dislocation climbs to the new oxide/metal interface location¹. Together with atomistic calculations, we identify that the pinning effect is associated with the non-local transport of metal atoms to fill vacancies at the dislocation core. These results provide mechanistic insight into solid-solid interfacial transformations and have significant implications in utilizing structural defects at buried interfaces to modulate mass transport and transformation kinetics.<br/><br/>Reference:<br/>¹X.H. Sun, D.X. Wu, L.F. Zou, S.D. House, X.B. Chen, M. Li, D.N. Zakharov, J.C. Yang, G.W. Zhou, “Misfit-dislocation induced stop-and-go kinetics of interfacial transformations”, Nature (in press, DOI: 10.1038/s41586-022-04880-1)