Diffusion of Cation Impurities through Ceria Grain Boundaries

Abstract

Cerium oxide (ceria) is widely used in relation to solid electrolytes in multiple high‐temperature devices, allowing metal components in contact to penetrate into the ceria, especially along the grain boundaries. However, few researchers have concentrated on the migration of metal cations at the operating temperatures (e.g., 600–750 °C) of these devices. Here, the diffusion and solubility of transition metals are investigated through acceptor‐doped ceria grain boundaries as a function of the temperature, pO2, dopant type, and doping concentration. The use of thin‐film samples with high grain boundary density levels and time‐of‐flight secondary ion mass spectrometry with ppb‐level chemical resolution enables an accurate analysis of the concentration profiles of metal species present inside the grain boundaries at such low temperatures. Ni, Fe, and Pt migrate unexpectedly rapidly, and the amounts and types of rare‐earth dopants have a considerable effect on the diffusion of the transition metal. Furthermore, transition metals (Mn, Fe, Co, Ni, and, Cu) are present at the grain boundaries at substantial solubility levels of ≈1022 cm−3, i.e., 1–2 orders of magnitude greater than in the bulk lattice. The observed dynamic behaviors of transition metals present a new perspective on the performance and durability of ceria‐containing applications.

Chemical Degradation of the La0.6Sr0.4Co0.2Fe0.8O3−δ/Ce0.8Sm0.2O2−δ Interface during Sintering and Cell Operation

“…The grain boundaries have more crystallographic defects than the bulk, implementing a facilitated pathway for cation diffusion [80]. Thus, cations diffuse preferentially through the grain boundaries; however, bulk diffusion is also possible, creating a concentration gradient from the grain boundaries to the bulk of the grain [81,82].…”

Enhanced Morphological Preservation and Redox Activity in Al-Incorporated NiFe2O4 for Chemical Looping Hydrogen Production

“…Rapid oxygen conduction pathways can also develop at grain boundaries, which can be faster than solid-state diffusion in the bulk. 38,39 Similar elucidation can be applied to the grain preserved Al doped Ni-ferrite system, thereby maintaining long-term performance.…”

Bulk and Short‐Circuit Anion Diffusion in Epitaxial Fe2O3 Films Quantified Using Buried Isotopic Tracer Layers

“…ToF SIMS has been used to track cation [ 28,29 ] and anion [ 28,30–33 ] diffusion in ionic solids. SIMS‐based techniques have been applied to measure area‐averaged grain boundary diffusion, [ 27,30,34 ] and recently, specialized measurements have been made on single grain boundaries with sub‐micron areal resolution. [ 15,35 ]…”

“…ToF SIMS has been used to track cation [28,29] and anion [28,[30][31][32][33] diffusion in ionic solids. SIMS-based techniques have been applied to measure area-averaged grain boundary diffusion, [27,30,34] and recently, specialized measurements have been made on single grain boundaries with sub-micron areal resolution. [15,35] Understanding the fundamental mechanisms of cation and anion diffusion in iron oxides is of broad interest because iron exhibits several stable oxide and hydroxide phases, each of which accommodates some level of cation and anion nonstoichiometry; [36] these complex point defect relationships dictate oxide diffusivity as a function of temperature and oxygen activity.…”