Faster Diffusion of Oxygen Along Dislocations in (La,Sr)MnO3+delta Is a Space-Charge Phenomenon
JM Borgers and J Kler and K Ran and E Larenz and TE Weirich and R Dittmann and RA De Souza, ADVANCED FUNCTIONAL MATERIALS, 31, 2105647 (2021).
In displaying accelerated oxygen diffusion along extended defects, (La,Sr)MnO3+delta is an atypical acceptor-doped perovskite-type oxide. In this study, O-18/O-16 diffusion experiments on epitaxial thin films of La0.8Sr0.2MnO3+delta 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. O-18 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+delta 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.
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