Selective formation of metastable polymorphs in solid-state synthesis.

Area of Science:

• Materials Science
• Solid-State Chemistry
• Crystallography

Background:

• Metastable polymorphs arise from complex thermodynamic and kinetic factors.
• Predictive synthesis methods for solution-based techniques are advancing, but solid-state methods lag.
• Controlling polymorph selectivity in solid-state reactions remains a challenge.

Purpose of the Study:

• To introduce a theoretical framework for predicting and controlling polymorph selectivity in solid-state reactions.
• To demonstrate the use of reaction energy as a key parameter for selecting metastable phases.
• To enable targeted synthesis of specific polymorphs via solid-state routes.

Main Methods:

• Developed a theoretical framework integrating thermodynamics and kinetics.
• Utilized in situ characterization techniques.
• Performed density functional theory (DFT) calculations.
• Investigated two synthesis pathways for Lithium Titanium Phosphate (LiTiOPO₄).

Main Results:

• Identified reaction energy as a critical factor influencing surface energy and metastable phase nucleation.
• Demonstrated precursor selection impacts reaction energy and thus polymorph outcome.
• Quantified conditions for experimental accessibility of metastable polymorphs.
• Successfully controlled LiTiOPO₄ polymorph synthesis via precursor choice.

Conclusions:

• The developed framework provides a general approach for targeted solid-state materials synthesis.
• Precursor selection offers a viable strategy for controlling polymorph nucleation.
• This approach has potential applications across diverse chemistries for selective polymorph synthesis.