Cation vacancies diminish the oxygen-vacancy diffusivity, raise the activation enthalpy, and cause the diffusivity to depend on oxygen activity.

In displaying accelerated oxygen diffusion along extended defects, (La,Sr)MnO 3+δ is an atypical acceptor-doped perovskite-type oxide. In this study, 18 O/ 16 O diffusion experiments on epitaxial thin films of La 0.8 Sr 0.2 MnO 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. 18 O 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] ≤ 973were 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 0.8 Sr 0.2 MnO 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.

The high-mobility, wide-bandgap perovskite oxide BaSnO 3 is taken as a model system to demonstrate that the native point defects present in un-doped, epitaxial thin films grown by hybrid molecular beam epitaxy can be identified and their concentrations at the ppm level determined quantitatively. An elevatedtemperature, multi-faceted approach is shown to be necessary: oxygen tracer diffusion experiments with secondary ion mass spectrometry analysis; molecular dynamics simulations of oxygen-vacancy diffusion; electronic conductivity studies as a function of oxygen activity and temperature; and Hall-effect measurements. The results indicate that the oxygen-vacancy concentration cannot be lowered below 10 17.3 cm −3 because of a background level of barium vacancies (of this concentration), introduced during film growth. The multi-faceted approach also yields the electron mobility over a wide temperature range, coefficients of oxygen surface exchange and oxygen-vacancy diffusion, and the reduction enthalpy. The consequences of the results for the lowest electron concentration achievable in BaSnO 3 samples, for the ease of oxide reduction and for the stability of reduced films with respect to oxidation, are discussed.