Three-dimensional quantification of composition and electrostatic potential at individual grain boundaries in doped ceria

Abstract

Despite typically comprising a small volume fraction, grain boundaries often limit many properties of ceramics for energy technologies. The localized charges present at grain boundaries affect local structure and composition which thus impact the ionic conductivities along with thermal, electrical, optical, magnetic, and mechanical properties. While theory regarding grain boundary effects has progressed, direct knowledge of the local chemistry and corresponding potential around individual boundaries remains elusive. Some model bicrystal systems have been well-characterized experimentally; however, the complexities of random grain boundary structures in bulk-prepared polycrystalline ceramics have prevented quantified analysis of the most commonly occurring types. Here, the three-dimensional quantification of oxygen and cation compositions around arbitrarily selected high-angle grain boundaries in a polycrystalline material as measured by atom probe tomography are used to extract nm-scale, quantitative values of the three-dimensional space-charge potentials around grain boundaries and are related to the observed macro-scale conductivities. We focus specifically on Nd-doped ceria, a well-known ion conducting oxide with significant energy applications. However, the techniques employed here are directly applicable to other technologically-relevant polycrystalline ceramics and create opportunities for correlating nano-scale composition with macro-scale properties for optimizing materials design, expanding progress in ionic chemistry theory, and refining simulations for “real-world” polycrystalline materials.