Structural complexity of simple Fe2O3 at high pressures and temperatures

Abstract

Although chemically very simple, Fe2O3 is known to undergo a series of enigmatic structural, electronic and magnetic transformations at high pressures and high temperatures. So far, these transformations have neither been correctly described nor understood because of the lack of structural data. Here we report a systematic investigation of the behaviour of Fe2O3 at pressures over 100 GPa and temperatures above 2,500 K employing single crystal X-ray diffraction and synchrotron Mössbauer source spectroscopy. Crystal chemical analysis of structures presented here and known Fe(II, III) oxides shows their fundamental relationships and that they can be described by the homologous series nFeO·mFe2O3. Decomposition of Fe2O3 and Fe3O4 observed at pressures above 60 GPa and temperatures of 2,000 K leads to crystallization of unusual Fe5O7 and Fe25O32 phases with release of oxygen. Our findings suggest that mixed-valence iron oxides may play a significant role in oxygen cycling between earth reservoirs.

Climate engineering by mimicking natural dust climate control: the iron salt aerosol method

“…when iron is cycled through the mantle at temperatures above 2500 K, Fe(III) is reduced to Fe(II) by the release of O 2 (Bykova et al, 2016). This phenomenon may be driven by the blackbody radiation containing a great fraction of photons with a wavelength shorter than 2 µm at and above this temperature level.…”

Stability and nature of the volume collapse of ε-Fe2O3 under extreme conditions

“…At present, the chemical composition of the Earth has a few major abundant elements, magnesium, aluminum, silicon and iron combined with hydrogen and/or oxygen or in their metallic state, i.e., iron–nickel alloys in the core. Due to an important presence of oxygen and iron in the Earth’s crust and the mantle, binary iron oxides and their derivative compounds can significantly influence the geodynamics of the Earth 4–7 . Consequently, several studies have been performed aiming to investigate the structural behavior of these phases focusing on their stability and their chemical and physical properties at extreme conditions, i.e., high pressure and high temperature (HPHT) 4,8–10 .…”

“…Hence, it is possible to conceive the presence of mineral phases with a high content of Fe 3+ /ΣFe even in the lowermost part of the lower mantle 1 . Indeed, recent studies reported the presence of stable Fe 3+ -rich oxides at conditions relevant for the whole lower mantle 4,9,10,14,15 .…”

High Pressure:One of the many Tools to Study Material Properties at Extreme Conditions

“…Even simple oxides of iron like hematite and magnetite decompose at 60-70 GPa and 2500 K to release large amounts of oxygen and form novel oxides of iron. These experiments suggest the presence of an oxygen-rich liquid in the deep interiors of the earth 24 . Thus it can be seen that these new studies on carbonic acid and iron oxides can be used in better geochemical modelling of the earth.…”