Elasticity and phase transformation at high pressure in coesite from experiments and first-principles calculations

Journal Article · Sun May 01 00:00:00 EDT 2016 · American Mineralogist

DOI:https://doi.org/10.2138/am-2016-5533· OSTI ID:1466808

Chen, Ting ^[1]; Wang, Xuebing ^[1]; Qi, Xintong ^[1]; Ma, Maining ^[2]; Xu, Zhishuang ^[2]; Li, Baosheng ^[1]

---

1. Stony Brook Univ., Stony Brook, NY (United States)
2. Univ. of Chinese Academy of Sciences, Beijing (China)

Here, the crystal structure and equation of state of coesite (space group C2/c) and its high pressure polymorph coesite-II (space group P2₁/n) under pressure have been studied using X-ray powder diffraction in a diamond anvil cell (DAC) up to 31 GPa at room temperature and first-principles calculations at 0 K up to 45 GPa. New diffraction peaks appear above 20 GPa, indicating the formation of coesite-II structure. The calculated enthalpies provide theoretical support for the pressure-induced phase transformation from coesite to coesite-II at ~21.4 GPa. Compared with coesite, the coesite-II structure is characterized by a ‘doubled’ b-axis and the breakdown of the linear Si1-O1-Si1 angle in coesite into two distinct angles - one is ~176°, close to linear, whereas the other decreases by 22° to 158°. Coesite is very anisotropic with the a-axis the shortest and twice more compressible than the b- and c-axis. By comparison, coesite-II is not so anisotropic with similar compressibilities in its a-, b-, and c-axis. As analyzed by a third-order Eulerian finite strain equation of state, the bulk modulus of coesite at 21.4 GPa is 182.3GPa, and that of coesite-II is 140.8 GPa, indicating that coesite-II is much more compressible than coesite. Furthermore, the existence of coesite-II in the coldest subduction zone will change the elasticity and anisotropic properties of the subducting materials dramatically.

• Research Organization: Stony Brook Univ., NY (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: NA0001815
• OSTI ID: 1466808
• Journal Information: American Mineralogist, Vol. 101, Issue 5; ISSN 0003-004X
• Publisher: Mineralogical Society of America
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
36 MATERIALS SCIENCE
coesite
phase transition
diamond anvil cell
first-principles calculation