Pressure-induced structural modulations in coesite

Wu, Ye and Liu, Hanyu and Huang, Haijun and Fei, Yingwei and Feng, Xiaolei and Redfern, Simon A. T. (2018) Pressure-induced structural modulations in coesite. Physical Review B, 98 (10). ISSN 2469-9950 DOI

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Silica phases, SiO2, have attracted significant attention as important phases in the fields of condensed-matter physics, materials science, and (in view of their abundance in the Earth's crust) geoscience. Here, we experimentally and theoretically demonstrate that coesite undergoes structural modulations under high pressure. Coesite transforms to a distorted modulated structure, coesite-II, at 22–25 GPa with modulation wave vector q=0.5b∗. Coesite-II displays further commensurate modulation along the y axis at 36–40 GPa and the long-range ordered crystalline structure collapses beyond ∼40GPa and starts amorphizing. First-principles calculations illuminate the nature of the modulated phase transitions of coesite and elucidate the modulated structures of coesite caused by modulations along the y-axis direction. The structural modulations are demonstrated to result from phonon instability, preceding pressured-induced amorphization. The recovered sample after decompression develops a rim of crystalline coesite structure, but its interior remains low crystalline or partially amorphous. Our results not only clarify that the pressure-induced reversible phase transitions and amorphization in coesite originate from structural modulations along the y-axis direction, but also shed light on the densification mechanism of silica under high pressure.

Item Type: Article
Uncontrolled Keywords: 2018AREP; IA73
Subjects: 03 - Mineral Sciences
Divisions: 03 - Mineral Sciences
08 - Green Open Access
Journal or Publication Title: Physical Review B
Volume: 98
Identification Number:
Depositing User: Sarah Humbert
Date Deposited: 20 Sep 2018 17:17
Last Modified: 20 Sep 2018 17:17

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