Kinetic Exploration of Nanoscale Polymorphs through Interface Energy Adjustment

Traditionally, the study of polymorphism has relied on thermodynamics and mass-averaged measurements. This work introduces a novel approach by combining kinetic analysis and statistical mechanics with electron microscopic imaging to observe phase transitions directly. We demonstrate a remarkable impact of the crystal size on the kinetic stability of polymorphs at nanoscale domains, enabling in situ manipulation of phase transitions at 298 K through interface energy adjustments by size reduction. Starting with the B1 NaI polymorph, we synthesized the previously unknown B2 polymorph upon size reduction. Starting from the CsCl liquid phase, we produced B1, previously described only above 749 K, and then B2 via quick martensitic transformation.