3D atomic imaging of advanced materials provides new insights into transitions such as liquids freezing into solids.

For nearly a century, scientists have relied on classical nucleation theory to explain how phase transitions such as freezing and condensation get started. The theory describes how small, ordered regions called nuclei emerge within disordered matter, and a central equation behind that picture has been supported by thousands of experiments.

But when UCLA-led researchers examined crystal formation atom by atom in three dimensions, the nuclei did not look the way the classical model predicts.