The Hydration Structure at Yttria-Stabilized Cubic Zirconia (110)-Water Interface with Sub-Ångström Resolution

Area of Science:

• Materials Science
• Surface Chemistry
• Nanotechnology

Background:

• Yttria-stabilized cubic zirconia (YSZ) is a crucial material in various applications, including solid oxide fuel cells and thermal barrier coatings.
• Understanding the behavior of YSZ surfaces in aqueous environments is vital for predicting and mitigating material degradation.
• The (110) surface is a representative crystallographic plane for YSZ, offering insights into general surface interactions.

Purpose of the Study:

• To elucidate the atomic-level interfacial hydration structure of the yttria-stabilized cubic zirconia (110) surface in contact with water.
• To identify the nature and arrangement of water molecules and potential species at the YSZ-water interface.
• To correlate the observed interfacial structure with surface defect chemistry and long-term material stability.

Main Methods:

• High-resolution X-ray reflectivity (HR-XRR) measurements were employed to probe the buried interface.
• Atomic-scale resolution (~0.5 Å) was achieved to precisely determine electron density profiles.
• Data analysis focused on modeling the electron density distribution to infer structural and chemical composition.

Main Results:

• The terminal surface layer exhibited reduced electron density, indicating metal depletion and intrinsic oxygen vacancies filled by water species.
• Two distinct adsorbed water layers were identified above the terminal layer.
• The first adsorbed layer showed high density and likely contained metal species, while the second layer comprised pure water.

Conclusions:

• The determined interfacial hydration structure is a complex, highly ordered arrangement of water and potential metal species.
• This ordered structure plays a role in the local equilibration of defective YSZ surfaces in water.
• The interfacial structure is proposed to regulate long-term degradation processes of yttria-stabilized cubic zirconia in aqueous environments.