Complex diffusion behavior of oxygen in nanocrystalline BaTiO3 ceramics

Area of Science:

• Materials Science
• Ceramic Engineering
• Solid-State Chemistry

Background:

• Barium titanate (BaTiO3) is a crucial perovskite material with applications in electronics.
• Understanding oxygen transport mechanisms is vital for optimizing BaTiO3 performance and longevity.
• Nanocrystalline ceramics exhibit unique properties compared to their microcrystalline counterparts due to increased grain boundary volume.

Purpose of the Study:

• To investigate oxygen diffusion pathways in dense, nanocrystalline BaTiO3 ceramics.
• To determine the influence of temperature and oxygen activity on oxygen transport.
• To elucidate the role of impurities and grain boundaries in oxygen diffusion.

Main Methods:

• Isotope exchange annealing using (18)O/(16)O.
• High-resolution depth profiling with Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS).
• Numerical solution of the diffusion equation to model isotope penetration.

Main Results:

• Observed unusual oxygen isotope penetration profiles with a flattened region near the surface.
• Quantitatively modeled the profiles using a diffusion equation with a surface-near diffusion coefficient increase.
• Attributed the enhanced diffusion to oxygen vacancies generated by chlorine impurity out-diffusion.

Conclusions:

• Nanocrystalline BaTiO3 exhibits enhanced oxygen transport near the surface.
• Chlorine impurities, originating from powder synthesis, significantly impact oxygen diffusion.
• This impurity-driven mechanism represents a key difference between nanocrystalline and microcrystalline ceramics.