DataSheet1_Stability and Thermoelasticity of Diaspore by Synchrotron X-ray Diffraction and Raman Spectroscopy.docx

The thermoelasticity and stability of diaspore (α-AlOOH, Al1.002Fe0.003OOH) were investigated in this study by in situ synchronous X-ray diffraction (XRD) and Raman spectroscopy methods at high pressure and high temperature conditions. The results indicate that diaspore is stable within the pressure and temperature (P-T) region examined in this study. With increasing pressure, the Raman peaks move toward the high wave number direction, the intensity of the Raman peaks increases, and the vibration mode of diaspore changes linearly. Pressure-volume data from in situ high-pressure XRD experiments were fitted by the third-order Birch-Murnaghan equation of state (EoS) with the zero-pressure unit-cell volume V0 = 118.15 (4) Å3, the zero-pressure bulk modulus KV0 = 153 (2) GPa, and its pressure derivative K'V0 = 2.4 (3). When K'V0 was fixed at 4, the obtained KV0 = 143 (1) GPa. The axial compressional behavior of diaspore was also fitted with a linearized third-order Birch-Murnaghan EoS, showing slight compression anisotropy with Ka0 = 137 (5) GPa, Kb0 = 169 (7) GPa and Kc0 = 178 (6) GPa. In addition, the temperature-volume data from in situ high-temperature XRD experiments were fitted by Fei’s thermal equation with the thermal expansion coefficients αV = 2.7 (2) × 10–5 K−1, αa = 1.13 (9) × 10–5 K−1, αb = 0.77 (5) × 10–5 K−1, and αc = 0.85 (9) × 10–5 K−1 for diaspore, which shows that diaspore exhibits slightly anisotropic thermal expansion. Furthermore, in situ synchrotron-based single-crystal XRD under simultaneously high P-T conditions indicates that the P-T stability of diaspore is up to ∼10.9 GPa and 700 K. Combined with previous results, we infer that diaspore can be subducted to ∼390 km under cold subduction conditions based on existing experimental data and is a good candidate for transporting water to the deep Earth.

本研究采用原位同步辐射X射线衍射（XRD）与拉曼光谱法，在高温高压条件下对硬水铝石（diaspore，α-AlOOH，Al₁.₀₀₂Fe₀.₀₀₃OOH）的热弹性与稳定性展开了探究。实验结果表明，在本研究考察的温压（P-T）范围内，硬水铝石始终保持稳定。随着压力升高，拉曼峰向高波数方向偏移，拉曼峰强度逐渐增强，且硬水铝石的振动模式呈线性变化。原位高压XRD实验获取的压力-体积数据，通过三阶Birch-Murnaghan状态方程（EoS）拟合得到如下参数：零压晶胞体积V₀=118.15(4) ų，零压体积模量K_V0=153(2) GPa，其压力导数K'_V0=2.4(3)。当将K'_V0固定为4时，拟合得到的K_V0为143(1) GPa。硬水铝石的轴向压缩行为通过线性化三阶Birch-Murnaghan状态方程进一步拟合，结果显示其存在微弱的压缩各向异性，拟合得到的各轴向体积模量分别为K_a0=137(5) GPa、K_b0=169(7) GPa及K_c0=178(6) GPa。此外，原位高温XRD实验获取的温度-体积数据，通过Fei热状态方程拟合得到硬水铝石的热膨胀系数：体膨胀系数α_V=2.7(2)×10⁻⁵ K⁻¹，轴向热膨胀系数α_a=1.13(9)×10⁻⁵ K⁻¹、α_b=0.77(5)×10⁻⁵ K⁻¹及α_c=0.85(9)×10⁻⁵ K⁻¹，表明硬水铝石呈现微弱的各向异性热膨胀特性。同步辐射原位高温高压单晶XRD实验进一步证实，硬水铝石的温压稳定上限约为10.9 GPa与700 K。结合已有研究成果，基于本实验数据我们推断：在冷俯冲条件下，硬水铝石可被俯冲至约390 km的地球深部，是将水输送至地球深部的优质候选载体。