Crystallization of SrAl₁₂O₁₉ Nanocrystals from Amorphous Submicrometer Particles.

Area of Science:

• Materials Science
• Crystallography
• Nanotechnology

Background:

• Transmission electron microscopy (TEM) has advanced crystallization studies, yet high-temperature annealing (HTA) pathways remain poorly understood.
• Metal oxide crystals, crucial for industry, are often produced via HTA, but controlling morphology and grain size is challenging.
• Understanding HTA crystallization is vital for designing and mass-producing high-performance metal oxide crystals.

Purpose of the Study:

• To investigate the crystallization pathway of amorphous SrAl12O19 (SA6) precursor particles under high-temperature annealing (HTA).
• To elucidate the roles of kinetic and thermodynamic factors in the evolution of crystal morphology and size during HTA.
• To demonstrate a nonclassical nucleation and growth process in detail.

Main Methods:

• Ex-situ transmission electron microscopy (TEM) was employed to analyze the transformation of amorphous SrAl12O19 particles at 1150 °C.
• Real-space imaging was used to track the step-by-step evolution of crystal structure and morphology.
• Analysis focused on identifying key stages including densification, domain formation, oriented attachment, and surface diffusion.

Main Results:

• The transformation of amorphous SrAl12O19 (SA6) spherical particles into nanosized hexagonal crystals at 1150 °C was observed.
• A detailed, step-by-step nonclassical nucleation and growth mechanism was identified, involving densification, crystallite domain formation, oriented attachment, surface nucleation, 2D growth, and surface diffusion.
• TEM images revealed a parent crystal guiding the lattice and morphology of interconnected platelets.

Conclusions:

• Kinetic and thermodynamic factors significantly influence crystal faceting and morphology evolution during HTA.
• The observed nonclassical crystallization pathway provides new insights into the formation of hexagonal platelet crystals from amorphous precursors.
• Controlling HTA processes can be optimized by understanding these detailed transformation mechanisms for improved crystal design and production.