Pressure-Induced Phase Transitions of Natural Brookite

Journal Article · 09 April 2019 · ACS Earth and Space Chemistry

DOI: https://doi.org/10.1021/acsearthspacechem.8b00213 · OSTI ID:1580877

Liu, Weixin ^[1]; Chen, Jian ^[1]; Zhang, Xiaoliang ^[1]; Yan, Jinyuan ^[2]; Hou, Mingqiang ^[3]; Kunz, Martin ^[2]; Zhang, Dongzhou ^[4]; Zhang, Hengzhong  ^[1]

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1. Center for High Pressure Science and Technology Advanced Research, Shanghai (China)
2. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
3. Center for High Pressure Science and Technology Advanced Research, Shanghai (China); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
4. Univ. of Hawaii at Manoa, Honolulu, HI (United States)

The structures and stabilities of the high-pressure phases of titania (TiO₂) are of great interest in the earth sciences, as these phases are the accessible analogs of component minerals in the earth's mantle. Brookite is a natural titania mineral, whose bulk phase is hard to synthesize in the laboratory, and its phase behavior at very high pressure remains unknown. Thus, in this work, using phase-pure natural brookite as the sample, we studied the phase transition of bulk brookite under compression up to ~60 GPa in three different pressure transmitting media. Results show that, at room temperature and in near hydrostatic conditions, brookite undergoes a series of transitions, i.e., brookite (~0-12 GPa) → TiO₂-II and minor rutile (~1-21 GPa) → baddeleyite (~12-60 GPa) → TiO₂-OI (~33-60 GPa). Taking into account that all transitions occur at finite rates and that solidification of a pressure medium can influence transition kinetics, we show that the observed transition sequence is consistent with the expected high-pressure phase stability of TiO₂ calculated from density functional theory. Finally, the knowledge obtained from this work may be used to infer the geological fate of brookite in nature.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: National Science Foundation (NSF); USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: AC02-05CH11231; AC02-06CH11357; EAR 11-57758; FG-02-94ER14466; EAR-1128799
• OSTI ID: 1580877
• Journal Information: ACS Earth and Space Chemistry, Vol. 3, Issue 5; ISSN 2472-3452
• Publisher: American Chemical SocietyCopyright Statement
• Country of Publication: United States
• Language: English