In situ observation of phase transformation in iron carbide nanocrystals

Le Thanh Cuong; Nguyen Duc Dung; Ta Quoc Tuan; Nguyen Thi Khoi; Pham Thanh Huy; Ngo Ngoc Ha

doi:10.1016/j.micron.2017.10.009

In situ observation of phase transformation in iron carbide nanocrystals

Micron. 2018 Jan:104:61-65. doi: 10.1016/j.micron.2017.10.009. Epub 2017 Oct 31.

Authors

Le Thanh Cuong¹, Nguyen Duc Dung², Ta Quoc Tuan³, Nguyen Thi Khoi³, Pham Thanh Huy³, Ngo Ngoc Ha⁴

Affiliations

¹ Electron Microscopy and MicroAnalysis Laboratory (BKEMMA), Advanced Institute of Science and Technology (AIST), Hanoi University of Science and Technology (HUST), No. 1 Dai Co Viet, Viet Nam.
² Electron Microscopy and MicroAnalysis Laboratory (BKEMMA), Advanced Institute of Science and Technology (AIST), Hanoi University of Science and Technology (HUST), No. 1 Dai Co Viet, Viet Nam. Electronic address: dung.nguyenduc@hust.edu.vn.
³ Nano Optoelectronics Laboratory, Advanced Institute of Science and Technology (AIST), HUST, No. 1 Dai Co Viet, Viet Nam.
⁴ Micro-nano Systems and Sensors Laboratory, International Training Institute for Materials Science (ITIMS), HUST, No. 1 Dai Co Viet, Viet Nam.

PMID: 29101880
DOI: 10.1016/j.micron.2017.10.009

Abstract

This paper reports on the in situ observation of phase transformation in an iron carbide nanocrystal encapsulated in a graphitic shell by means of high resolution transmission electron microscopy (HR-TEM). A Fe₇C₃ nanocrystal in orthorhombic (o-Fe₇C₃) structure with carbon graphitic cover is captured at the initial time of the experiment. Under the projection of a high-energy electron beam (200kV), the graphitic carbon layer evaporates gradually and structural changes in orthorhombic (o-Fe₇C₃) crystal manifests simultaneously. Specifically, changes in crystal direction happens first and then the crystal structure switching between orthorhombic and hexagonal (h-Fe₇C₃) follows. Details analysis and conclusive evidences of the phase structure and transformation are presented and discussed. The appearance of o-Fe₇C₃ structure is captured for about 92min over 100min of observation, indicating the preference of o-Fe₇C₃ form over h-Fe₇C₃ form.

Keywords: In situ TEM; Iron carbide; Nanocrystals; Phase transformation; Structural stability.