Resolving Diverse Oxygen Transport Pathways Across Sr‐Doped Lanthanum Ferrite and Metal‐Perovskite Heterostructures

Abstract

Perovskite structured transition metal oxides are important technological materials for catalysis and solid oxide fuel cell applications. Their functionality often depends on oxygen diffusivity and mobility through complex oxide heterostructures, which can be significantly impacted by structural and chemical modifications, such as doping. Further, when utilized within electrochemical cells, interfacial reactions with other components (e.g., Ni‐ and Cr‐based alloy electrodes and interconnects) can influence the perovskite's reactivity and ion transport, leading to complex dependencies that are difficult to control in real‐world environments. Here, this work uses isotopic tracers and atom probe tomography to directly visualize oxygen diffusion and transport pathways across perovskite and metal‐perovskite heterostructures, that is, (Ni‐Cr coated) Sr‐doped lanthanum ferrite (La0.5Sr0.5FeO3; LSFO). Annealing in 18O2(g) results in elemental and isotopic redistributions through oxygen exchange (OE) in the LSFO while Ni‐Cr undergoes oxidation via multiple mechanisms and transport pathways. Complementary density functional theory calculations at experimental conditions provide rationale for OE reaction mechanisms and reveal a complex interplay of different thermodynamic and kinetic drivers. These results shed light on the fundamental coupling of defects and oxygen transport in an important class of catalytic materials.

Synthesis, Processing, and Use of Isotopically Enriched Epitaxial Oxide Thin Films

“…By exposing the needle-shaped specimen to 18 O at elevated temperature in situ in a reaction chamber connected via UHV transfer to the APT analysis chamber, diverse oxygen transport pathways across the system can be measured by isotopically resolved APT without air exposure that might further redistribute the anion tracers (Figure 6). 14 We found that a substantial fraction of the O in the (La,Sr)FeO 3 film, ∼84%, was exchanged for 18 O during the anneal (400 °C, 4 h, 3 mbar 99% enriched 18 O 2 ). This rapid oxygen exchange was attributed to an anion-vacancy-mediated diffusion mechanism and facilitated by the large surface area of the film in the needle geometry.…”