Collective Modes and Defects Implicated in Phase Transitions

by Tommy on 25/02/2017

Here is yet another brilliant study.

http://www.nature.com/articles/ncomms14462

In situ study on atomic mechanism of melting and freezing of single bismuth nanoparticles, Yingxuan Li, Ling Zang, Daniel L. Jacobs, Jie Zhao, Xiu Yue and Chuanyi Wang, Nature Communications 8, 14462 (13 February 2017), doi:10.1038/ncomms14462

Experimental study of the atomic mechanism in melting and freezing processes remains a formidable challenge. We report herein on a unique material system that allows for in situ growth of bismuth nanoparticles from the precursor compound SrBi2Ta2O9 under an electron beam within a high-resolution transmission electron microscope (HRTEM). Simultaneously, the melting and freezing processes within the nanoparticles are triggered and imaged in real time by the HRTEM. The images show atomic-scale evidence for point defect induced melting, and a freezing mechanism mediated by crystallization of an intermediate ordered liquid. During the melting and freezing, the formation of nucleation precursors, nucleation and growth, and the relaxation of the system, are directly observed. Based on these observations, an interaction–relaxation model is developed towards understanding the microscopic mechanism of the phase transitions, highlighting the importance of cooperative multiscale processes.

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