Understanding Topochemical Microcrystal Conversion in Molten Salt to Produce High-Aspect-Ratio Perovskites Particles

Area of Science:

• Materials Science
• Crystallography
• Nanotechnology

Background:

• Highly anisotropic platelet-shaped particles, particularly perovskites, are crucial for advanced structural and functional applications due to their opto- and piezoelectric properties.
• Topochemical microcrystal conversion (TMC) in molten salt is a scalable method for fabricating these particles, but lacks precise control over particle size and aspect ratio.
• Understanding the reaction mechanisms of TMC is essential for tailoring particle morphology and optimizing material properties.

Purpose of the Study:

• To investigate the nucleation and growth mechanisms of anisotropic bismuth sodium titanate (Bi_0.5Na_0.5TiO₃ or BNT) particles during TMC.
• To gain insights into how controlling reaction conditions, specifically TiO₂ deficiencies, influences BNT particle morphology.
• To develop a method for producing high-aspect-ratio BNT platelets with improved properties.

Main Methods:

• Employed in situ time-resolved synchrotron X-ray diffraction to monitor the TMC process of Bi_0.5Na_0.5TiO₃ (BNT) from Bi₄Ti₃O₁₂ (BiT) templates.
• Varied TiO₂ deficiencies during the TMC reaction to study their effect on nucleation and growth.
• Fabricated thin BNT-based platelets to validate the growth model and assess aspect ratio enhancement.

Main Results:

• Demonstrated that precise control over nucleation and initial crystallite growth dictates the final BNT particle morphologies.
• Produced BNT platelets with a 1.2- to 2.1-times higher median aspect ratio compared to previous studies.
• Fabricated thin Bi_0.5Na_0.5TiO₃-BaTiO₃ platelets exhibiting significantly enhanced median (up to 17) and 90th percentile (up to 41) aspect ratios, surpassing those of the BiT templates.

Conclusions:

• The study provides new insights into the TMC reaction mechanisms, highlighting the critical role of nucleation and early growth stages in determining particle morphology.
• The developed approach enables enhanced control over the aspect ratio of perovskite platelets, leading to superior material characteristics.
• This work advances the understanding and fabrication of high-aspect-ratio perovskite platelets for diverse functional applications.