96Zr Tracer Diffusion in AZro3 (A = Ca, Sr, Ba)

Abstract

Cation tracer diffusion in polycrystalline AZrO3 (A = Ca, Sr, Ba) perovskites was studied at 1300–1500 °C in air using the stable isotope 96Zr. Thin films of 96ZrO2 were deposited on polished ceramic pellets by drop casting of an aqueous precursor solution containing the tracer. The pellets were subjected to thermal annealing, and the isotope depth profiles were measured by secondary ion mass spectrometry. Two distinct regions with different slopes in the profiles enabled to assess separately the lattice and grain boundary diffusion coefficients using Fick’s second law and Whipple–Le Clair’s equation. The cation diffusion along grain boundaries was 4–5 orders of magnitude faster than the corresponding lattice diffusion. The magnitude of the diffusivity of Zr4+ was observed to increase with decreasing size of the A-cation in AZrO3, while the activation energy for the diffusion was comparable 435 ± 67, 505 ± 56, and 445 ± 45 and kJ·mol−1 for BaZrO3, SrZrO3, and CaZrO3, respectively. Several diffusion mechanisms for Zr4+ were considered, including paths via Zr- and A-site vacancies. The Zr4+ diffusion coefficients reported here were compared to previous data reported on B-site diffusion in perovskites, and Zr4+ diffusion in fluorite-type compounds.