Faster Diffusion of Oxygen Along Dislocations in (La,Sr)MnO_3+δ Is a Space‐Charge Phenomenon

Abstract In displaying accelerated oxygen diffusion along extended defects, (La,Sr)MnO_3+δ is an atypical acceptor‐doped perovskite‐type oxide. In this study, ¹⁸O/¹⁶O diffusion experiments on epitaxial thin films of La_0.8Sr_0.2MnO_3+δ and molecular dynamics (MD) simulations are combined to elucidate the origin of this phenomenon for dislocations: Does diffusion occur along dislocation cores or along space‐charge tubes? Transmission electron microscopy studies of the films revealed dislocations extending from the surface. ¹⁸O penetration profiles measured by secondary ion mass spectrometry indicated (slow) bulk diffusion and faster diffusion along dislocations. Oxygen tracer diffusivities obtained for temperatures 873 ≤ T [K] ≤ 973 were over two orders of magnitude higher for dislocations than for the bulk. The activation enthalpy of oxygen diffusion along dislocations, of (2.95 ± 0.21) eV, is surprisingly high relative to that for bulk diffusion, (2.67 ± 0.13) eV. This result militates against fast diffusion along dislocation cores. MD simulations confirmed no accelerated migration of oxide ions along dislocation cores. Faster diffusion of oxygen along dislocations in La_0.8Sr_0.2MnO_3+δ is thus concluded to occur within space‐charge tubes in which oxygen vacancies are strongly accumulated. Reasons for and the consequences of space‐charge zones at extended defects in manganite perovskites are discussed.