Pressure-induced structural and electronic changes of iron in peridotitic glasses

Data on the electronic state and local environment of Fe as a function of pressure (P) are scarce because of experimental challenges of synthesising relevant compositions for the early Earth. This proposal aims to measure Fe in peridotitic glasses, synthesised under different oxygen fugacity (fO2), using X-ray Absorption spectroscopy up to 150 GPa in a diamond anvil cell. Using high resolution energy scans at the Fe K-edge, we will measure its pre-edge feature (i.e. redox, spin state), as well as the extended region above the edge (i.e. mean bond length). Combined with our recent high pressure Mössbauer spectroscopy, we will identify the different spin states of Fe in peridotitic glasses and establish a calibration for the absolute proportions of Fe2+ and Fe3+ therein, using the XANES method. Hence, we aim to determine the relative stabilities of Fe2+ and Fe3+ as a function of P, and whether the fO2 at the surface of a planet depends upon its mass, affecting the Earth’ evolution.

受限于合成早期地球相关组分所面临的实验挑战，关于铁（Fe）的电子态及其局域环境随压强（P）变化的相关数据十分匮乏。本研究计划借助金刚石压腔（DAC）内的X射线吸收光谱，在最高150 GPa的压强条件下，对不同氧逸度（fO2）条件下合成的橄榄岩质玻璃中的铁元素进行表征。通过对铁K边开展高分辨能量扫描，我们将获取其预边特征（即氧化还原态与自旋态）以及边后扩展区域的信息（即平均键长）。结合我们近期开展的高压穆斯堡尔光谱实验，我们将通过X射线吸收近边结构（XANES）方法，识别橄榄岩质玻璃中铁的不同自旋态，并建立该体系中二价铁（Fe²+）与三价铁（Fe³+）绝对占比的校准曲线。据此，我们旨在明确二价铁与三价铁的相对稳定性随压强的变化规律，并探究行星表面的氧逸度是否与其质量相关，进而影响地球的演化过程。