Structural transformations on vitrification in the fragile glass-forming system CaAl2O4

Area of Science:

• Materials Science
• Solid State Chemistry
• Structural Analysis

Background:

• Calcium aluminate (CaAl2O4) is a fragile glass-forming material.
• Understanding the structural evolution from liquid to glass is crucial for materials design.

Purpose of the Study:

• To elucidate the structural changes in CaAl2O4 during the liquid-to-glass transition.
• To investigate structural modifications on multiple length scales upon quenching.

Main Methods:

• Neutron diffraction with Calcium (Ca) isotope substitution.
• Measurements performed on laser-heated, aerodynamically levitated liquid (1973 K) and glass (300 K).
• Analysis aided by molecular dynamics simulations.

Main Results:

• Quenching breaks down liquid AlO5 polyhedra and threefold coordinated oxygen atoms.
• Glass structure is dominated by a corner-sharing network of AlO4 tetrahedra.
• Branched chains of edge- and face-sharing Ca-centered polyhedra form, indicating cationic ordering.
• Calcium coordination number changes slightly from 6.0(2) in liquid to 6.4(2) in glass.

Conclusions:

• The transition involves significant polyhedral reorganization from AlO5 to AlO4.
• Cationic ordering occurs on an intermediate length scale in the glass.
• Neutron diffraction with isotope substitution is effective for studying liquid and glass structures.