Three-dimensional imaging of grain boundaries via quantitative fluorescence X-ray tomography analysis

Visualizing the composition of grain networks is key for understanding the structure evolution and functional properties of composite materials. Here, X-ray fluorescence tomography, coupled with an absorption correction algorithm, reveals mechanistic insights in the phase transformations and transport properties of a mixed ionic-electronic conductor.

Three-dimensional visualization of material composition within multiple grains and across complex networks of grain boundaries at nanoscales can provide new insight into the structure evolution and emerging functional properties of the material for diverse applications. Here, using nanoscale scanning X-ray fluorescence tomography, coupled with an advanced self-absorption correction algorithm developed in this work, we analyze the three-dimensional gain distributions and compositions in a Ce0.8Gd0.2O2-delta-CoFe2O4 mixed ionic-electronic conductor system with high accuracy and statistical significance. Our systematic investigation reveals an additional emergent phase and uncovers highly intriguing composition stability ranges for the multiple material phases within this system. The presented visualization of composition variations across complex interfaces, supported by our quantitative composition analysis, discloses mechanistic pathways of the diverse phase transformations occurring in the material synthesis, providing insights for the optimization of transport properties in the mixed ionic-electronic conductor system.