In Situ Synchrotron Radiation and Neutron Diffraction Reveal A-Site Substitution Pathways and Structural...

Area of Science:

• Materials Science
• Solid State Chemistry
• Nanotechnology

Background:

• Layered MAX phases combine metallic and ceramic properties for demanding applications.
• Understanding atomic-scale A-site substitution is crucial for designing robust MAX phases.

Purpose of the Study:

• To synthesize a heterostructured MAX phase with improved corrosion resistance.
• To elucidate the atomic-scale mechanisms of A-site substitution in MAX phases.

Main Methods:

• Lewis molten-salt treatment of Mo2Ga2C precursor.
• Rietveld refinements of X-ray and neutron diffraction data.
• In situ synchrotron radiation X-ray diffraction and density functional theory calculations.

Main Results:

• Successfully synthesized a heterostructured MAX phase (Mo2SnC and Mo2Ga0.5Sn0.5C).
• Uncovered a multi-step A-site substitution pathway involving intermediate phases and layer transformation.
• Demonstrated significantly improved corrosion resistance in acidic, alkaline, and saline solutions.

Conclusions:

• Ga-to-Sn substitution drives A-site reconstruction and chemical optimization.
• Revealed novel A-site dynamics in MAX phase formation.
• Provided a design strategy for creating chemically robust MAX phases for harsh conditions.