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In-Situ Observation of the Formation of Fibrous Sulfur under High Pressure

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journal contribution
posted on 22.05.2019, 00:00 by Kaiyuan Shi, Bing Liu, Yingju Wu, Zitai Liang, Xiaoyu Wang, Lei Su, Yanlong Wang, Li Zhang, Guoqiang Yang, Yang Zhang, Chenlong Xie, Zhisheng Zhao
Sulfur (S) possesses the largest number of allotropes among all elements. Herein, the formation of fibrous S via two different synthesis paths (path 1: S-I → S-II → fibrous S; path 2: S-I → liquid S → a-S → S-II → fibrous S) was investigated through in-situ Raman spectroscopy and synchrotron X-ray diffraction (XRD) analyses in a diamond anvil cell (DAC). Raman spectroscopy revealed the kinetic transformations from S-I to S-II and liquid S to S-II under high temperature and high pressure, and an intermediate amorphous phase was observed during the phase transition of liquid S to S-II. By decompressing S-II to ∼0.9 GPa at room temperature, the fibrous S would be formed and recovered to ambient conditions regardless of the paths. However, the difference of synthesis paths would result in the distinct microstructures and mechanical properties of fibrous S in bulk polycrystalline forms synthesized by a large press. In particular, the bulk sample synthesized from path 2 was composed of numerous aligned ultrafine S nanofibers. The presence of intermediate amorphous phase and the microstructure difference of fibrous S might account for various contradictions among previously reported results.