Crystallization from solution is commonly described by classical nucleation theory, although this ignores that crystals often form via disordered nanostructures. As an alternative, the classical theory remains widely used in a “multistep” variant, where the intermediate nanostructures merely introduce additional thermodynamic parameters. However, this variant still requires validation by experiments addressing indeed proper time and spatial scales (millisecond, nanometer). Here, 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. We find that the self-confinement by an amorphous precursor slows down crystal growth by 2 orders of magnitude once the crystal size reaches the amorphous particle size (∼3 nm). Thus, not only the thermodynamic properties of transient amorphous nanostructures but also their spatial distribution determine crystal nucleation.

中文翻译：

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纳米结构非晶前驱体中氧化铁纳米粒子的自限制成核。

从溶液中结晶通常用经典的成核理论来描述，尽管这忽略了晶体通常是通过无序的纳米结构形成的。作为替代，经典理论仍然广泛用于“多步”变体中，其中中间纳米结构仅引入了额外的热力学参数。但是，此变体仍需要通过针对确实合适的时间和空间范围（毫秒，纳米）的实验进行验证。在这里，我们使用原位X射线散射来确定磁铁矿结晶的机理，尤其是确定成核如何在无定形前体中以纳米级传播。我们发现，一旦晶体尺寸达到无定形粒径（〜3 nm），无定形前体的自约束将晶体生长减慢2个数量级。从而，