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Fe4O5 and its solid solutions in several simple systems

机译：Fe4O5及其在几种简单系统中的固体溶液

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摘要

Experiments at high pressures and temperatures reveal the stability of a Fe4O5-type structured phase in several simple chemical systems. On the one hand, the Fe4O5 end-member is stable in the presence of SiO2-rich phases, including stishovite, but contains ≤0.01 Si cations per formula unit. This indicates that Si is essentially excluded from this phase. On the other hand, the Fe4O5 phase can form solid solutions with Mg and Cr and can coexist with silicate phases at the high P–T conditions expected in the transition zone of the mantle (i.e. >~9 GPa). It can coexist with both wadsleyite and Mg-rich ringwoodite and can contain at least 25 mol% Mg2Fe2O5 component. The Fe4O5 phase always contains the least amount of Mg in any given mineral assemblage. Cr-bearing Fe4O5 has been synthesised with up to 46 mol% Fe2Cr2O5 component and can coexist with spinel and/or hematite-eskolatite solid solutions. Substitution of Mg and Cr for Fe2+ and Fe3+, respectively, leads to variations in Fe3+/∑Fe from the ideal value of 0.5 for the Fe4O5 end-member composition, which can influence its redox stability. These cations also have contrasting effects on the unit-cell parameters, which indicate that they substitute into different sites. This initial study suggests that Fe4O5-type structured phases may be stable over a range of P–T–fO2 conditions and bulk compositions, and can be important in understanding the post-spinel phase relations in a number of chemical systems relevant to the Earth’s transition zone. Thus, the presence of even small amounts of Fe3+ could alter the expected phase relations in peridotitic bulk compositions by stabilising this additional phase.
机译：高压和高温下的实验揭示了Fe4O5型结构相在几种简单化学系统中的稳定性。一方面，Fe4O5末端成员在存在富含SiO2的相（包括辉石）的情况下是稳定的，但每个配方单元含≤0.01的硅阳离子。这表明从该阶段基本上排除了Si。另一方面，Fe4O5相可以与Mg和Cr形成固溶体，并且可以在地幔过渡带（即>〜9 GPa）中预期的高P-T条件下与硅酸盐相共存。它可以与沃兹利特石和富含Mg的林木共存，并且可以包含至少25 mol％的Mg2Fe2O5组分。在任何给定的矿物组合物中，Fe4O5相始终包含最少的Mg。含铬的Fe4O5已被合成为具有高达46mol％的Fe2Cr2O5成分，并且可以与尖晶石和/或赤铁矿-钙铁矿固溶体共存。用Mg和Cr代替Fe2 +和Fe3 +会导致Fe3 + / ∑Fe从Fe4O5末端成员组成的理想值0.5的变化而来，这可能影响其氧化还原稳定性。这些阳离子对晶胞参数也有相反的影响，表明它们可以取代成不同的位点。这项初步研究表明，Fe4O5型结构化相在一系列P–T–fO2条件和整体组成下可能是稳定的，并且对于理解与地球过渡相关的许多化学系统中的尖晶石后相关系可能很重要。区。因此，即使少量的Fe3 +的存在也可以通过稳定该附加相来改变钙钛矿块状组合物中的预期相关系。

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