Shape Preserving Single Crystal to Amorphous to Single Crystal Polymorphic Transformation Is Possible

Area of Science:

• Solid-state chemistry
• Crystallography
• Materials science

Background:

• Crystalline materials often exist as polymorphs, undergoing solid-solid transitions under varying temperature or pressure.
• Understanding the precise mechanisms of these polymorphic transformations remains a significant challenge due to their typically rapid rates.
• Current mechanistic insights are often inferred by comparing pre- and post-transition crystal structures, limiting detailed understanding.

Purpose of the Study:

• To investigate the mechanism of polymorphic phase transitions in crystalline materials.
• To challenge the prevailing assumption that crystallinity is maintained during shape-preserving polymorphic transitions.
• To elucidate the role of intermediate phases in solid-solid transformations.

Main Methods:

• Single crystal X-ray diffraction analysis
• Observation of slow solid-solid phase transitions in ZnCl2(1,3-diethylimidazole-2-thione)2 polymorphs
• Characterization of intermediate amorphous phases

Main Results:

• A polymorphic transformation in ZnCl2(1,3-diethylimidazole-2-thione)2 was observed to be unusually slow.
• The transformation proceeded via an amorphous intermediate phase.
• Shape preservation was maintained throughout the single crystal to single crystal transformation.

Conclusions:

• The study reveals a novel mechanism for polymorphic phase transitions involving an amorphous intermediate.
• This finding challenges the long-held view that crystallinity is preserved during shape-preserving solid-solid transformations.
• The slow rate of this specific transition enabled detailed mechanistic insights previously unattainable.