Discontinuity in crystal lattice and composition at grain boundaries play an important role in materials properties. Indeed in many instances grain boundary engineering may alter transport and kinetic properties by several orders of magnitude. Especially, in fluorite-structured oxide materials, ion diffusion and surface exchange at grain boundaries are strongly influenced by atomic structure and defect distribution.In this talk, we present atomic scale imaging of oxygen columns and show quantitative analysis of column occupancy in a single grain-boundary of a YSZ bicrystal. We report experimental observation and determination of oxide-ion vacancy concentration near the ?13 (510)/[001] symmetric tilt grain-boundary using aberration-corrected TEM operated under negative spherical aberration coefficient imaging condition. We show significant oxygen deficiency due to segregation of oxide-ion vacancies near the grain-boundary core with half-width <0.6 nm. Electron energy loss spectroscopy measurements with scanning TEM indicated increased oxide-ion vacancy concentration at the grain boundary core. Furthermore, oxide-ion density distribution near a grain boundary simulated by molecular dynamics agreed well with experimental results. Such column-by-column quantification of defects in functional materials may lead to new insights to engineer grain boundaries designed for specific functionalities.Microscopic studies of oxygen vacancy distribution across grain boundaries are corroborated with oxygen surface exchange characteristics, which usually govern the overall performance of solid oxide fuel cells. Accordingly, we report on the role of grain boundaries in enhancing oxygen incorporation in oxide ion conductors. Oxygen isotope exchange measurements were carried out using high spatial resolution secondary ion mass spectrometry (nano-SIMS). Surface mapping of the 18O distribution by SIMS shows high activity along surface grain boundaries, suggesting that these boundary regions provide preferential pathways for oxide ion incorporation into YSZ. The nano-SIMS observations are supported by impedance spectroscopy measurements conducted on polycrystalline YSZ membranes with surface grains engineered for different sizes.

Microscopic and spectroscopic examination of oxygen vacancy distribution and oxygen exchange at YSZ grain boundaries

247th National Meeting (2014)

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