北京高压科学研究中心地球深部条件下羟基氧化铁FeOOH在地球深部条件下超离子态转变数据集（2020-2021）

通过研究在地球深部条件下羟基氧化铁（FeOOH）的转化过程，发现核幔边界的含水矿物黄铁矿型（Pyrite-type, Py）FeO₂Hₓ在100–121 GPa、1500–1700 ℃条件下，原位测试显示其电导率增大了两倍。高温促使氢离子在FeO₂的晶格中自由移动，FeO₂Hₓ会发生晶态-超离子态转变，这是地幔深部首次发现的超离子态含水矿物。在北京高压科学研究中心完成了DAC装样、四电极铺设、激光加热实验和理论计算工作。将羟基氧化铁放入DAC样品腔中，高纯氩气作为静水压介质（PTM）可减小体系压差，采用1070 nm连续波掺镱光纤激光器进行激光加热。原位拉曼光谱使用自行搭建的拉曼平台进行，激发波长为633 nm（功率＜1 mW），采集范围为1000–4000 cm⁻¹，分辨率为1.0 cm⁻¹，激光聚焦光斑约为10 μm。为消除原位高压拉曼光谱中的荧光背景和宇宙射线干扰，每个谱图均重复测试10次。通过Origin软件处理得到原位拉曼光谱数据。高温高压电导率测试采用四探针范德堡法进行电阻率测量；使用高精度源表和纳伏表测量样品电阻，测量不确定度小于0.1%。在高压条件下，样品难以维持理想的平整状态。样品表面的粗糙度与不平整度会对四电极的配对读数产生影响，因此电阻的总误差通过R₁₂与R₃₄的差值估算得出。对于高温下的电子电导率测量，采用连续激光加热方式，将样品温度升至预设最高温度。在每个设定温度下，保持加热5分钟，并在此期间记录电阻值并进行时间平均处理。在整个加热循环过程中，温度波动控制在±50 K范围内。在美国阿贡国家实验室先进光子源（APS）的16-ID-B和13-ID-D线站进行了同步辐射原位高压XRD测试，利用同步辐射原位衍射和时间分辨衍射揭示了体系中氢原子组成随加热时间的变化。通过实验结果与计算模拟相互验证，基于FPMD模拟数据，通过计算获得速度自相关函数、质子扩散系数、EC值和IC值，证明了地球深部条件下超离子态的转变过程。该工作为研究地球内部的热量传导机制提供了重要依据，有助于更准确地模拟地球内部的热传递过程，了解地球内部的温度分布和演化，理解板块构造运动的驱动力和地球内部的动力学机制。

By investigating the transformation process of iron oxyhydroxide (FeOOH) under Earth's deep interior conditions, it was found that the pyrite-type (Py) FeO₂Hₓ, a hydrous mineral at the core-mantle boundary (CMB), exhibited a twofold increase in electrical conductivity in in-situ measurements conducted at 100–121 GPa and 1500–1700 ℃. High temperature promotes the free movement of hydrogen ions within the FeO₂ crystal lattice, triggering a crystalline-to-superionic phase transition in FeO₂Hₓ; this represents the first discovered superionic hydrous mineral in the deep mantle.

All DAC sample loading, four-electrode layout, laser heating experiments, and theoretical calculations were completed at the Center for High Pressure Science and Technology Advanced Research (HPSTAR, Beijing). Iron oxyhydroxide was loaded into the DAC sample chamber, with high-purity argon used as the quasi-hydrostatic pressure medium (PTM) to reduce the pressure variation in the system. A 1070 nm continuous-wave ytterbium-doped fiber laser was employed for laser heating.

In-situ Raman spectroscopy was performed using a custom-built Raman platform, with an excitation wavelength of 633 nm (power <1 mW), an acquisition range of 1000–4000 cm⁻¹, a spectral resolution of 1.0 cm⁻¹, and a laser focused spot size of approximately 10 μm. To eliminate fluorescence background and cosmic ray interference in in-situ high-pressure Raman spectra, each spectrum was measured repeatedly 10 times. The in-situ Raman spectroscopic data were processed using Origin software.

High-pressure high-temperature (HPHT) electrical conductivity testing adopted the four-probe van der Pauw method for resistivity measurement; a high-precision source meter and nanovoltmeter were used to measure the sample resistance, with a measurement uncertainty of less than 0.1%. Under high-pressure conditions, it is difficult to maintain an ideal flat state for samples. The surface roughness and unevenness of the sample will affect the paired readings of the four electrodes, so the total error of the resistance was estimated by the difference between R₁₂ and R₃₄. For electronic electrical conductivity measurements at high temperatures, continuous laser heating was used to raise the sample temperature to the predetermined maximum temperature. At each set temperature, heating was maintained for 5 minutes, during which the resistance values were recorded and subjected to time-averaging processing. Throughout the entire heating cycle, the temperature fluctuation was controlled within ±50 K.

Synchrotron radiation in-situ high-pressure X-ray diffraction (XRD) measurements were carried out at beamlines 16-ID-B and 13-ID-D of the Advanced Photon Source (APS) at Argonne National Laboratory in the United States. Synchrotron radiation in-situ diffraction and time-resolved diffraction were utilized to reveal the variation of hydrogen atomic composition with heating time in the system.

Cross-validation between experimental results and computational simulations was performed; based on first-principles molecular dynamics (FPMD) simulation data, the velocity autocorrelation function, proton diffusion coefficient, electronic conductivity (EC), and ionic conductivity (IC) were calculated, proving the superionic phase transition process under Earth's deep interior conditions.

This work provides an important basis for studying the heat conduction mechanisms within the Earth, facilitating more accurate simulations of the Earth's internal heat transfer processes, understanding the temperature distribution and evolution of the Earth's interior, and comprehending the driving forces of plate tectonics and the dynamical mechanisms of the Earth's interior.