Surface strain often controls properties of the material including charge
transport and chemical reactivity. Localized surface strain is measured with
atomic resolution on (111) ceria nanoparticle surfaces using environmental
transmission electron microscopy under different redox conditions. Density
Functional Theory (DFT) coupled with TEM image simulations have been used for
aid in interpreting the experimental data. Oxygen vacancy creation/annihilation
introduces strain at surface and near surface regions on cation sublattice.
Static and fluxional strainmaps are generated from images at these different
conditions and compared. While fluxional strain is highest at locations
associated with unstable vacancies at active sites, highly inhomogeneous static
strain fields comprising of alternating tensile/compressing strain is seen at
surface and subsurfaces linked to the presence of stable oxygen vacancies.
Interestingly, both stable and unstable oxygen vacancies are found within a few
atomic spacing of each other on the same surface. The static strain pattern
depends on the ambient inside TEM. Oxidizing environments tend to lower vacancy
concentrations at the surface whereas a highly reducing environment created
using high electron dose creates oxygen vacancies everywhere (bulk and
surfaces) in the nanoparticle