Journal
CRYSTAL GROWTH & DESIGN
Volume 17, Issue 12, Pages 6291-6296Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.cgd.7b00977
Keywords
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Funding
- Ministry of Education and Science of Russian Federation [14.B25.31.0032, MK-3417.2017.5, K3-2017-026]
- RFBR [17-42-190308 r_a]
- DCO
- National Science Foundation - Earth Sciences [EAR - 1634415]
- Department of Energy-GeoSciences [DE-FG02-94ER14466]
- DOE Office of Science [DE-AC02-06CH11357]
- [0330-2016-0006]
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The importance for the global carbon cycle, the P-T phase diagram of CaCO3 has been under extensive investigation since the invention of the high-pressure techniques. However, this study is far from being completed. In the present work, we show the existence of two new high-pressure polymorphs of CaCO3. The crystal structure prediction performed here reveals a new polymorph corresponding to distorted aragonite structure and named aragonite-II. In situ diamond anvil cell experiments confirm the presence of aragonite-II at 35 GPa and allow identification of another high-pressure polymorph at 50 GPa, named CaCO3-VII. CaCO3-VII is a structural analogue of CaCO3-P2(1)/c-1, predicted theoretically earlier. The P-T phase diagram obtained based on a quasi-harmonic approximation shows the stability field of CaCO3-VII and aragonite-II at 30-50 GPa and 0-1200 K. Synthesized earlier in experiments on cold compression of calcite, CaCO3-VI was found to be metastable in the whole pressure temperature range.
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