Universität zu Köln

Koch-Mueller, Monika, Jahn, Sandro ORCID: 0000-0002-2137-8833, Birkholz, Natalie, Ritter, Eglof and Schade, Ulrich ORCID: 0000-0002-4194-2235 (2016). Phase transitions in the system CaCO3 at high P and T determined by in situ vibrational spectroscopy in diamond anvil cells and first-principles simulations. Phys. Chem. Miner., 43 (8). S. 545 - 562. NEW YORK: SPRINGER. ISSN 1432-2021

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Abstract

The stability of the high-pressure CaCO3 calcite (cc)-related polymorphs was studied in experiments that were performed in conventional diamond anvil cells (DAC) at room temperature as a function of pressure up to 30 GPa as well as in internally heated diamond anvil cells (DAC-HT) at pressures and temperatures up to 20 GPa and 800 K. To probe structural changes, we used Raman and FTIR spectroscopy. For the latter, we applied conventional and synchrotron mid-infrared as well as synchrotron far-infrared radiation. Within the cc-III stability field (2.2-15 GPa at room temperature, e.g., Catalli and Williams in Phys Chem Miner 32(5-6):412-417, 2005), we observed in the Raman spectra consistently three different spectral patterns: Two patterns at pressures below and above 3.3 GPa were already described in Pippinger et al. (Phys Chem Miner 42(1):29-43, 2015) and assigned to the phase transition of cc-IIIb to cc-III at 3.3 GPa. In addition, we observed a clear change between 5 and 6 GPa that is independent of the starting material and the pressure path and time path of the experiments. This apparent change in the spectral pattern is only visible in the low-frequency range of the Raman spectra-not in the infrared spectra. Complementary electronic structure calculations confirm the existence of three distinct stability regions of cc-III-type phases at pressures up to about 15 GPa. By combining experimental and simulation data, we interpret the transition at 5-6 GPa as a re-appearance of the cc-IIIb phase. In all types of experiments, we confirmed the transition from cc-IIIb to cc-VI at about 15 GPa at room temperature. We found that temperature stabilizes cc-VI to lower pressure. The reaction cc-IIIb to cc-VI has a negative slope of -7.0 x 10(-3) GPa K-1. Finally, we discuss the possibility of the dense cc-VI phase being more stable than aragonite at certain pressure and temperature conditions relevant to the Earth's mantle.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Koch-Mueller, Monika UNSPECIFIED UNSPECIFIED UNSPECIFIED Jahn, Sandro UNSPECIFIED orcid.org/0000-0002-2137-8833 UNSPECIFIED Birkholz, Natalie UNSPECIFIED UNSPECIFIED UNSPECIFIED Ritter, Eglof UNSPECIFIED UNSPECIFIED UNSPECIFIED Schade, Ulrich UNSPECIFIED orcid.org/0000-0002-4194-2235 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-265044
DOI:	10.1007/s00269-016-0815-8
Journal or Publication Title:	Phys. Chem. Miner.
Volume:	43
Number:	8
Page Range:	S. 545 - 562
Date:	2016
Publisher:	SPRINGER
Place of Publication:	NEW YORK
ISSN:	1432-2021
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language HIGH-PRESSURE BEHAVIOR; HIGH-TEMPERATURE; CRYSTAL-STRUCTURE; CALCITE-III; X-RAY; MAGNESITE; CARBONATES; ARAGONITE; DOLOMITE; SPECTRA Multiple languages Materials Science, Multidisciplinary; Mineralogy Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/26504