Pressure-Induced Phase Transitions in δ-(Al,Fe)OOH [δ-(Al,Fe)OOH的高压相变]

作者：Wang B.; Xiao W.; Song M.

来源：Chinese Journal of High Pressure Physics, 2021, 35(6): 061201.

DOI：10.11858/gywlxb.20210765

• $
• delta $-(Al,Fe)OOH
• High pressure
• Phase transition
• Spin crossover
• X-ray diffraction

δ-(Al,Fe)OOH is regarded as a potential water carrier to core-mantle conditions, thus its high pressure structural behavior is important for understanding water circulation in the Earth's interior. In this study, the compression behaviour of 8 mol.% Fe-bearing δ phase (δ-Fe8) is investigated using diamond anvil cell combined with synchrotron X-ray diffraction. The obtained pressure-volume (p-V) data show that δ-Fe8 experiences phase transitions from order to disorder of hydrogen and high spin to low spin of iron in the pressure range from ambient pressure to 78 GPa. The order to disorder transition of hydrogen takes place at 9.7 GPa characterized by the subtle kinks in the p-V profiles and the inversion of pressure dependence of a/c and b/c axial ratios, which accompany with a change in the crystallographic symmetry from P21nm to Pnnm. The isostructural iron spin crossover occurs between 31.5 and 39.5 GPa accompanied by 2% volume collapse. The compressional parameters are derived from fitting of p-V data using Birch-Murnaghan equation of state. The mixed-spin state of δ-Fe8 within the spin crossover region is treated as an ideal solid solution of the high spin and low spin state, then the fraction of low spin state is obtained by fitting experimental data. The calculated bulk moduli and bulk sound velocity soften across spin crossover, indicating that an accumulation of δ-Fe8 in middle part of lower mantle possibly leads to low bulk velocity anomalies. The linear relations between ferric content and structural transition pressure in δ-(Al,Fe)OOH are given with the combination of this study and previous results.

• 单位
  同位素地球化学国家重点实验室; 中国科学院大学