"Non-classical” nucleation of oxide nanoparticles in solution: implications on structure control
Abstract
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