Diffusion Kinetics of Ba Cations in Perovskite BaTiO3: A Combined Tracer Diffusion and Metadynamics Study

Abstract Tracer diffusion experiments and metadynamics (MetaD) simulations were used to study the diffusion of Ba cations in the cubic phase of the perovskite oxide BaTiO3. 130BaTiO3 thin films were used as diffusion sources to introduce barium tracer diffusion profiles into single-crystal samples at temperatures 1348 ≤ T/K ≤ 1498. The 130Ba profiles were determined by time-of-flight secondary ion mass spectrometry, and then analyzed to yield Ba tracer diffusion coefficients (DBa*). MetaD simulations were performed in order to obtain barium-vacancy diffusion coefficients (DvBa) for selected vacancy mechanisms as a function of temperature. DvBa is predicted to be increased significantly by an adjacent oxygen vacancy, and even more by an adjacent titanium vacancy. From the combined consideration of DBa* and DvBa, we conclude that Ba diffusion in these samples occurred most probably by the migration of defect associates, and not by the migration of isolated barium vacancies. More generally, our analysis draws attention to the benefits of using diffusivities rather than activation enthalpies to interpret diffusion data.