Pressure-induced large volume collapse and possible spin transition in HP-PdF2-type FeCl2

IF 1.2 4区 地球科学 Q4 MATERIALS SCIENCE, MULTIDISCIPLINARY
Yao Yao, Xi Liu, Xueyan Du, Lili Zhang, Hongsheng Yuan
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Abstract

Iron hydroxide FeO2Hx (x ≤ 1) and ferrous iron chloride FeCl2 can adopt the HP-PdF2-type (space group: \(P{a_{\overline 3 }}\), Z = 4) structure in the lowermost mantle, potentially contributing to the geochemical cycles of hydrogen and chlorine within Earth’s deep interior, respectively. Here we investigate the high-pressure behavior of HP-PdF2-type FeCl2 by X-ray diffraction (XRD) and Raman measurements in laser-heated diamond anvil cells. Our results show that HP-PdF2-type FeCl2 can be formed at 60‒67 GPa and 1650‒1850 K. Upon cold decompression, the diffraction peaks at pressures above 10 GPa can be indexed to the HP-PdF2-type structure. Intriguingly, the calculated cell volumes reveal a remarkable decrease of ΔV / V = ∼ 14% between 36 and 40 GPa, which is possibly caused by a pressure-induced spin transition of Fe2+ (HS: high-spin → LS: low-spin). We also observe distinct changes in Raman spectra at 33‒35 GPa, practically coinciding with the onset pressures of isostructural phase transition in XRD results. Our observations combined with previous studies conducted at megabar pressures suggest that HP-PdF2-type FeCl2, with a wide pressure stability range, if present in subducting slabs, could facilitate the transport of chlorine from the middle lower mantle to the outer core.

Abstract Image

HP-PdF2- 型 FeCl2 中压力诱导的大体积坍缩和可能的自旋转变
氢氧化铁FeO2Hx(x≤1)和氯化亚铁FeCl2在最下地幔中可以采用HP-PdF2-型(空间群:\(P{a_{/overline3}}/),Z = 4)结构,可能分别促进地球深部内部氢和氯的地球化学循环。在此,我们通过在激光加热的金刚石砧单元中进行 X 射线衍射 (XRD) 和拉曼测量,研究了 HP-PdF2 型 FeCl2 的高压行为。我们的结果表明,HP-PdF2-型 FeCl2 可在 60-67 GPa 和 1650-1850 K 条件下形成。冷减压后,压力高于 10 GPa 时的衍射峰可与 HP-PdF2- 型结构相联系。耐人寻味的是,计算得到的晶胞体积显示,在 36 至 40 GPa 之间,ΔV / V = ∼ 14% 显著下降,这可能是由于压力引起的 Fe2+ 自旋转变(HS:高自旋 → LS:低自旋)造成的。我们还观察到拉曼光谱在 33-35 GPa 时的明显变化,实际上与 XRD 结果中等结构相变的起始压力相吻合。我们的观察结果与之前在兆帕压力下进行的研究相结合,表明 HP-PdF2- 型 FeCl2 具有较宽的压力稳定性范围,如果存在于俯冲板块中,则可促进氯从中下地幔向外核的迁移。
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来源期刊
Physics and Chemistry of Minerals
Physics and Chemistry of Minerals 地学-材料科学:综合
CiteScore
2.90
自引率
14.30%
发文量
43
审稿时长
3 months
期刊介绍: Physics and Chemistry of Minerals is an international journal devoted to publishing articles and short communications of physical or chemical studies on minerals or solids related to minerals. The aim of the journal is to support competent interdisciplinary work in mineralogy and physics or chemistry. Particular emphasis is placed on applications of modern techniques or new theories and models to interpret atomic structures and physical or chemical properties of minerals. Some subjects of interest are: -Relationships between atomic structure and crystalline state (structures of various states, crystal energies, crystal growth, thermodynamic studies, phase transformations, solid solution, exsolution phenomena, etc.) -General solid state spectroscopy (ultraviolet, visible, infrared, Raman, ESCA, luminescence, X-ray, electron paramagnetic resonance, nuclear magnetic resonance, gamma ray resonance, etc.) -Experimental and theoretical analysis of chemical bonding in minerals (application of crystal field, molecular orbital, band theories, etc.) -Physical properties (magnetic, mechanical, electric, optical, thermodynamic, etc.) -Relations between thermal expansion, compressibility, elastic constants, and fundamental properties of atomic structure, particularly as applied to geophysical problems -Electron microscopy in support of physical and chemical studies -Computational methods in the study of the structure and properties of minerals -Mineral surfaces (experimental methods, structure and properties)
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