  Grain boundaries (GBs) are a prolific microstructural feature that dominates
the functionality of a wide class of materials. The change in functionality at
a GB is a direct result of unique local atomic arrangements, different from
those in the grain, that have driven extensive experimental and theoretical
studies correlating atomic-scale GB structures to macroscopic electronic,
infrared-optical, and thermal properties. Here, we examine a SrTiO3 GB using
atomic-resolution aberration-corrected scanning transmission electron
microscopy (STEM) and ultra-high-energy-resolution monochromated electron
energy-loss spectroscopy (EELS), in conjunction with density functional theory
(DFT) calculations. This combination enables the direct correlation of the GB
structure, composition, and chemical bonding with atomic vibrations within the
GB dislocation-cores. We observe that nonstoichiometry and changes in
coordination and bonding at the GB leads to a redistribution of vibrational
states at the GB and its dislocation-cores relative to the bounding grains. The
access to localized vibrations within GBs provided by ultrahigh
spatial/spectral resolution EELS correlated with atomic coordination, bonding,
and stoichiometry and validated by theory, provides a direct route to
quantifying the impact of individual boundaries on macroscopic properties.
