The diminished conductivity of pristine grain boundaries in oxide‐ion conducting electrolytes, such as (Ce,Gd)O2 and (Zr,Y)O2, is widely interpreted with the Mott‐Schottky space‐charge model, or less frequently, with the Gouy‐Chapman space‐charge model. Although routinely applied to the entire compositional range of solid solutions, from dilute to concentrated, these models, being based on the Poisson‐Boltzmann formalism, are limited in their range of validity to dilute solutions of point defects. Analyzing the grain‐boundary properties of concentrated solid solutions with such models is expected to lead to errors and inconsistencies. In this study, we employ Poisson‐Cahn theory to analyze literature data for the grain‐boundary resistance of CeO2‐Gd2O3 materials as a function of Gd concentration. Poisson‐Cahn theory combines the Cahn‐Hilliard theory of inhomogeneous systems with the Poisson equation of electrostatics and it is valid over the entire compositional range. We treat the realistic case of a restricted equilibrium: Gd accumulation profiles are frozen‐in from sintering temperatures, while the oxygen‐vacancy distributions are in equilibrium at sintering and (much lower) measurement temperatures. Data for the grain‐boundary resistance are also analyzed with the standard analytical expressions from the Mott‐Schottky and Gouy‐Chapman models. Outside the domain of their validity, these expressions are found to perform poorly. In general, we emphasize the importance of treating the interfacial properties of concentrated solid solutions with physically appropriate theories.
As pace-charge theory applicable to concentrated solid solutions (Poisson-Cahn theory) was applied to describe quantitatively as afunction of temperature and oxygen partial pressure published data obtained by in situ X-ray photoelectron spectroscopy( XPS) for the concentration of Ce 3+ (the reactive species) at the surface of the oxide catalyst Ce 0.8 Sm 0.2 O 1.9 .I nc ontrast to previous theoretical treatments, these calculations clearly indicate that the surface is positively charged and compensated by an attendant negative spacecharge zone.T he high space-charge potential that develops at the surface (> 0.8 V) is demonstrated to be hardly detectable by XPS measurements because of the short extent of the spacecharge layer.T his approach emphasizes the need to take into account defect interactions and to allowd eviations from local charge neutrality when considering the surfaces of oxide catalysts.
As pace-charge theory applicable to concentrated solid solutions (Poisson-Cahn theory) was applied to describe quantitatively as afunction of temperature and oxygen partial pressure published data obtained by in situ X-ray photoelectron spectroscopy( XPS) for the concentration of Ce 3+ (the reactive species) at the surface of the oxide catalyst Ce 0.8 Sm 0.2 O 1.9 .I nc ontrast to previous theoretical treatments, these calculations clearly indicate that the surface is positively charged and compensated by an attendant negative spacecharge zone.T he high space-charge potential that develops at the surface (> 0.8 V) is demonstrated to be hardly detectable by XPS measurements because of the short extent of the spacecharge layer.T his approach emphasizes the need to take into account defect interactions and to allowd eviations from local charge neutrality when considering the surfaces of oxide catalysts.
A new data-driven interacting-defect model has quantitatively described the nanoscopic composition of high solute concentrations at grain boundaries in ion-conducting ceramics. The successful model is a data-driven Cahn-Hilliard methodology for interfaces and surfaces, introduced and demonstrated in this report. The model is applied to high spatial resolution composition data gathered at grain boundaries in calcium-doped ceria. The statistical methodology for the data-driven procedure shows definitively that gradient terms are required to quantitatively describe the local grain boundary composition data. The model additionally shows co-accumulation of negatively-charged acceptor dopants and positivelycharged oxygen vacancies at the interface, which is qualitatively in accordance with atom probe tomography evidence in acceptor-doped ceria.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.