Faster Diffusion of Oxygen Along Dislocations in (La,Sr)MnO3+δ Is a Space-Charge Phenomenon

Abstract

In displaying accelerated oxygen diffusion along extended defects, (La,Sr)MnO3+δ is an atypical acceptor-doped perovskite-type oxide. In this study, 18O/16O diffusion experiments on epitaxial thin films of La0.8Sr0.2MnO3+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 La0.8Sr0.2MnO3+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.