Fe spin transition in the Earth's mantle: insight from X-ray Raman scattering and X-ray absorption spectroscopy

矿物中的Fe ~（2+）（3d ~ 6电子组态）和Fe ~（3+）（3d ~ 5）在环境条件下均处于高自旋电子态，在地幔压力和温度下可能发生从高自旋（HS）到低自旋（LS）的跃迁。自旋状态的变化对铁镁矿物的结构、物理和化学性质以及依赖于这些性质的地幔动力学过程都有相当大的影响。该项目的目的是提供新的实验见解，在HS-LS过渡期间的电子变化及其与局部和晶体结构变化的关系。通过应用X射线拉曼散射（XRS）和X射线吸收光谱（包括X射线吸收光谱），将获得新的见解。共振X射线发射光谱，RXES）。这两种技术提供了有价值的见解的电子和局部结构的Fe M，L和K-边缘的测量。XRS还允许研究例如O K边缘和Si、Mg L边缘。在菱铁矿和镁菱铁矿的样品上已经证明了在高达50 GPa的压力下进行XRS测量的可行性。项目期间将完成菱镁矿-菱铁矿固溶体的研究工作。最终的目标是调查更复杂的矿物布里奇曼石，这是下地幔最丰富的阶段之一。新获得的数据将被用来解决有关该矿物相的自旋转变机制的争议。根据测量数据，将结合基于DFT的计算机模拟开发结构模型。最后，将评估结果对低地球地幔的影响。

Both, Fe2+ (3d6-electronic configuration) and Fe3+ (3d5) in minerals are in high spin electronic state at ambient conditions and may undergo transitions from the high spin (HS) to the low spin (LS) state at pressures and temperatures expected in the Earth mantle. The change in spin state has considerable impact on structural, physical and chemical properties of Fe-Mg minerals as well as on geodynamic processes in the Earth mantle that depend on these. The aim of this project is to provide new experimental insights to the electronic changes during the HS-LS transition and their relationship to changes in the local and crystal structure. New insights will be gained by application of X-ray Raman scattering (XRS) and X-ray absorption spectroscopy (incl. Resonant X-ray emission spectroscopy, RXES). Both techniques provide valuable insights to the electronic and local structure by measurements of the Fe M, L and K-edges. XRS also allows for investigation of the, e.g. O K-edge and Si, Mg L-edge. Feasibility of XRS measurements at pressures up to 50 GPa has been shown on samples of siderite and magnesio-siderite. During the project, the work on the magnesite-siderite solid solution will be completed. Final goal is the investigation of the more complex mineral bridgmanite, which is one of the most abundant phases of the lower mantle. The newly obtained data will be used to solve the controversy regarding the mechanism of the spin transition in this mineral phase. From the measured data, structural models will be developed by combination with DFT-based computer simulations. Finally, the implications of the results for the lower Earth's mantle will be assessed.