Kavli Affiliate: David T. Limmer
| First 5 Authors: Sophia B. Betzler, Daewon Lee, Sam Oaks-Leaf, Colin Ophus, Lin-Wang Wang
| Summary:
Strain at interfaces may profoundly impact the microstructure and properties
of materials; thus, it is a major consideration when designing and engineering
materials. Dislocation formation is a commonly known mechanism to release
mismatch strain at solid-solid interfaces. However, it is still unclear about
how materials accommodate interfacial strain under drastically accelerated
structural transformation kinetics, since it is extremely challenging to
directly observe the atomic structure evolution of fast-propagating interfaces.
Utilizing liquid phase transmission electron microscopy (TEM), we have achieved
atomic-scale imaging of hydrogen-induced phase transformations of palladium
nanocrystals with different transformation speeds. Our observation reveals that
the fast phase transformation occurs with an expanded interface of mixed
$alpha$- and $beta$-$mathrm{PdH}_x$ phases, and tilting of (020) planes to
accommodate mismatch strain. In contrast, slow phase transformations lead to
sharp interfaces with slipping misfit dislocations. Our kinetic Monte Carlo
simulations show that fast phase transformation pushes the system
far-from-equilibrium, generically roughening the interface; however, a smooth
boundary minimizes strain near-equilibrium. Unveiling the atomic pathways of
transformations from near-equilibrium to far-from-equilibrium, which was
previously possible only computationally, this work holds significant
implications for engineering microstructure of materials through modulating
solid-solid transformations in a wide range of kinetics.
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