Multistep nucleation visualized during solid-state crystallization.

Area of Science:

• Materials Science
• Physical Chemistry
• Crystallography

Background:

• Classical nucleation theory has long been debated, with recent arguments for a nonclassical "two-step" mechanism.
• Understanding the microscopic kinetics and thermodynamics of nonclassical nucleation remains experimentally challenging.

Purpose of the Study:

• To investigate the complex mechanisms of early-stage crystallization in solid-state nucleation.
• To elucidate the intermediate steps and driving forces in nonclassical nucleation pathways.

Main Methods:

• Utilized in situ transmission electron microscopy for real-time observation of solid-state nucleation.
• Employed experimental and theoretical analyses to understand microscopic kinetics and thermodynamics.

Main Results:

• Observed that early-stage crystallization follows a nonclassical pathway with multiple metastable states preceding stable nucleus formation.
• Identified intermediate steps including spinodal decomposition, mass transport, and structural oscillations between crystalline and amorphous states.
• Determined that energetic favorability drives the observed sequence of events.

Conclusions:

• Solid-state crystallization can proceed via a complex nonclassical mechanism involving multiple metastable states.
• Findings provide new insights into modern nucleation theory, challenging existing models.
• Offers potential avenues for advanced materials design through understanding crystallization pathways.