High-Pressure Iron-Sulfur Compounds and their Implications for the Mineralogy of the Sulfur-Bearing Iron Cores

Details High-Pressure Iron-Sulfur Compounds and their Implications for the Mineralogy of the Sulfur-Bearing Iron Cores High-Pressure Iron-Sulfur Compounds and their Implications for the Mineralogy of the Sulfur-Bearing Iron Cores

Apr 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja.....3652k&link_type=abstract

EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #3652

Physics

Scientific paper

Sulfur is considered to be the possible light element that alloys with iron in the terrestrial planetary cores. Prior to 1997, end-members Fe and FeS are used to model the cores because no intermediate compounds between Fe and FeS were found. Recent high-pressure experiments revealed that at least three new iron-sulfur compounds, Fe3S2, Fe2S, and Fe3S, were formed at high pressures [Fei et al. Science 275, 1621-1623, 1997; Fei et al. Am. Mineral. 85, 1830-1833, 2000]. Because the physical properties of a planetary core are governed by its mineralogy, it is essential to fully characterize these compounds. We synthesized Fe3S,Fe3S2 and Fe2S iron-sulfur compounds at 22 GPa and 950 to 1050 oC and characterized them by X-ray powder diffraction, electron microprobe analyses and transmission electron microscopy. Fe3S is a quenchable phase in the Fe-S system. It is isostructural with Cr3P. The X-ray diffraction patterns for the Fe3S2 and Fe2S samples are complicated and cannot be indexed with a single phase. TEM and X-ray diffraction measurements show that the samples are extremely fine grained and multi phase products. Fe2S exists as a phase in the Fe-S system, but it is unstable at ambient condition. The TEM measurements revealed that it decomposes to Fe3S and FeS. However, the Fe2S phase was partially survived during quenching. X-ray diffraction data indicated that Fe2S exists in two polymorphs. Both polymorphs have the hexagonal cell. Their possible structure analogs are Ti2P and Fe2P. The Fe3S2 phase is of non-stoichiometric nature. The exact composition of the Fe3S2 phase synthesized in this study is close to Fe3.2S2. It is isostructural with TiP0.63 (=Ti3.18P2). During quenching it partially decomposes to FeS and Fe2S. The stability fields and the structures of the Fe2S and Fe3.2S2 phases need to be further investigated by in-situ measurements. From the TEM measurements, we also found single crystals of cubic Fe2S3 in the quenched Fe3.2S2 sample. However, the quantity of this phase is very small (1 wt% based on the quantitative phase analysis).

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