Correlation between structure, surface defect chemistry and ¹⁸O/¹⁶O exchange for La₂Mo₂O₉ and La₂(MoO₄)₃

Area of Science:

• Materials Science
• Surface Chemistry
• Solid-State Chemistry

Background:

• Lanthanum molybdates (La₂Mo₂O₉ and La₂(MoO₄)₃) are synthesized via solid-state reactions.
• Dense ceramics are prepared from these powders for advanced applications.

Purpose of the Study:

• To analyze the chemical composition and elemental charge states in the subsurface of lanthanum molybdate ceramics.
• To investigate the kinetics of oxygen exchange on the surface of these materials.

Main Methods:

• Solid-state reaction method for powder synthesis.
• X-ray photoelectron spectroscopy (XPS) for surface analysis under varying vacuum and oxygen partial pressures.
• Kinetic analysis using a two-step model for oxygen adsorption and incorporation.

Main Results:

• High-resolution XPS spectra for La 3d, Mo 3d, and O 1s states were obtained and analyzed.
• Oxygen adsorption (r_a) and incorporation (r_i) rates were calculated.
• Correlations between oxide surface defect chemistry and oxygen exchange rates were established.

Conclusions:

• Surface defect chemistry significantly impacts the rates of oxygen adsorption and incorporation in lanthanum molybdates.
• The findings provide insights into the surface processes governing oxygen exchange in these ceramic materials.