Oxygen surface exchange and diffusion in mayenite single crystal.

Area of Science:

• Materials Science
• Solid State Chemistry
• Crystallography

Background:

• Mayenite (Ca12Al14O33±δ) is a complex oxide with potential applications in various fields.
• Understanding oxygen surface exchange and diffusion is crucial for optimizing material performance.
• Previous studies have proposed models for oxygen diffusion in mayenite, but some aspects remain debated.

Purpose of the Study:

• To investigate oxygen surface exchange and diffusion in Ca12Al14O33±δ single crystals.
• To develop and apply a novel in situ method for analyzing oxygen transport mechanisms.
• To clarify the surface heterogeneity and diffusion behavior of mayenite, particularly in the 750 °C to 850 °C range.

Main Methods:

• Utilized a unique in situ method based on isotope equilibration in the gas phase.
• Analyzed oxygen surface exchange rates and diffusion coefficients.
• Employed single crystal samples of Ca12Al14O33±δ.

Main Results:

• The interphase exchange rate and oxygen diffusion coefficient align with existing data.
• The employed method successfully isolated contributions from various exchange types, enabling surface heterogeneity estimation.
• Results contradict previous literature, indicating the 750 °C to 850 °C range is not an intermediate region for two coexisting oxygen diffusion types.

Conclusions:

• The study provides the first quantitative estimation of mayenite surface heterogeneity.
• The findings challenge established models regarding oxygen diffusion mechanisms in mayenite within the studied temperature range.
• A new model is proposed, explaining temperature-dependent properties based on near-surface layer stability.