Multiphase transformation and Ostwald's rule of stages during crystallization of a metal phosphate

• Published in: Nature physics Vol. 5; no. 1; pp. 68 - 73
• Main Authors: Chung, Sung-Yoon, Kim, Young-Min, Kim, Jin-Gyu, Kim, Youn-Joong
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.01.2009; Nature Publishing Group
• Subjects: Atomic; Classical and Continuum Physics; Colloids; Complex Systems; Condensed Matter Physics; Crystallization; Electron microscopes; Electron microscopy; Experiments; High temperature; Kinetics; Mathematical and Computational Physics; Molecular; Optical and Plasma Physics; Physics; Physics and Astronomy; Theoretical
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/nphys1148

Although the classical picture of crystallization depicts a simple and immediate transformation from an amorphous to a crystalline phase, it has been argued that, in selected systems, intermediate metastable phases exist before a stable state is finally reached. However, most experimental observations have been limited to colloids and proteins, for which the crystallization kinetics are fairly slow and the size is comparatively large. Here, we demonstrate for the first time in an inorganic compound at an atomic scale that an amorphous phase transforms into a stable crystalline state via intermediate crystalline phases, thus directly proving Ostwald’s rule of stages. Through in situ high-resolution electron microscopy in real time at a high temperature, we show the presence of metastable transient phases at an atomic scale during the crystallization of an olivine-type metal phosphate. These results suggest a new description for the kinetic pathway of crystallization in complex inorganic systems. High-resolution electron microscope images collected in real time demonstrates the occurrence of multiple intermediary phases during the crystallization of a metal phosphate. The observations represent the first atomic-scale demonstration of Wilhelm Ostwald’s ‘rule of stages’ proposed over a century ago.