  Solid-state transformation is often accompanied by mechanical
expansion/compression, due to their volume change and structural evolution at
interfaces at the atomic scale. However, these two types of dynamics are
usually difficult to monitor in the same time. In this work, we use in-situ
transmission electron microscopy to directly study the reduction transformation
at the AgCl-Ag interface. Three stages of lattice fluctuations were identified
and correlated to the structural evolution. During the steady state, a
quasi-layered growth mode of Ag in both vertical and lateral directions were
observed due to the confinement of AgCl lattices. The development of planar
defects and depletion of AgCl are respectively associated with lattice
compression and relaxation. Topography and structure of decomposing AgCl was
further monitored by in-situ scanning transmission electron microscopy. Silver
species are suggested to originate from both the surface and the interior of
AgCl, and be transported to the interface. Such mass transport may have enabled
the steady state and lattice compression in this volume-shrinking
transformation.
