"Non-classical” nucleation of oxide nanoparticles in solution: implications on structure control
Résumé
Crystallization from solution is commonly described by classical nucleation theory [1], although this ignores that crystals often form via disordered nanostructures [2]. As an alternative, the classical theory remains widely used in a “multi-step” variant, where the intermediate nanostructures merely introduce additional thermodynamic parameters [3]. But this variant still requires validation by experiments addressing indeed proper time and spatial scales (ms, nm). We used in situ X-ray scattering to determine the mechanism of magnetite crystallization and in particular how nucleation propagates at the nanometer scale within amorphous precursors [4]. We find that the self-confinement by an amorphous precursor slows down crystal growth by two orders of magnitude once the crystal size reaches the amorphous particle size (c.a. 3 nm). Thus, not only the thermodynamic properties of transient amorphous nanostructures, but also their spatial distribution determine crystal nucleation
