Boulard E, Harmand M, Guyot F, Lelong G, Morard G, Cabaret D, Boccato S, Rosa A D, Briggs R, Pascarelli S, Fiquet G
Sorbonne Université, Muséum National d'Histoire Naturelle, UMR CNRS 7590, IRD Institut de Minéralogie, Physique des Matériaux et Cosmochimie - IMPMC 4 Place Jussieu 75005 Paris France.
European Synchrotron Radiation Facility Grenoble France.
Geophys Res Lett. 2019 Feb 16;46(3):1348-1356. doi: 10.1029/2019GL081922. Epub 2019 Feb 14.
Recent experiments have demonstrated the existence of previously unknown iron oxides at high pressure and temperature including newly discovered pyrite-type FeO and FeOH phases stable at deep terrestrial lower mantle pressures and temperatures. In the present study, we probed the iron oxidation state in high-pressure transformation products of FeOOH goethite by in situ X-ray absorption spectroscopy in laser-heated diamond-anvil cell. At pressures and temperatures of ~91 GPa and 1,500-2,350 K, respectively, that is, in the previously reported stability field of FeOH, a measured shift of -3.3 ± 0.1 eV of the Fe K-edge demonstrates that iron has turned from Fe to Fe. We interpret this reductive valence change of iron by a concomitant oxidation of oxygen atoms from O to O, in agreement with previous suggestions based on the structures of pyrite-type FeO and FeOH phases. Such peculiar chemistry could drastically change our view of crystal chemistry in deep planetary interiors.
最近的实验已经证明，在高压和高温下存在以前未知的铁氧化物，包括新发现的在地球深部下地幔压力和温度下稳定的黄铁矿型FeO和FeOH相。在本研究中，我们通过激光加热金刚石砧室中的原位X射线吸收光谱法，探测了FeOOH针铁矿高压转变产物中的铁氧化态。分别在约91 GPa的压力和1500 - 2350 K的温度下，即在先前报道的FeOH稳定域中，Fe K边测量到的-3.3±0.1 eV的位移表明铁已从Fe转变为Fe。我们通过氧原子从O到O的伴随氧化来解释铁的这种还原价态变化，这与基于黄铁矿型FeO和FeOH相结构的先前建议一致。这种特殊的化学性质可能会彻底改变我们对深部行星内部晶体化学的看法。
