AUTHOR=Huang Shijie , Xu Jingui , Liu Daorong , Li Bo , Ye Zhilin , Chen Wei , Kuang Yunqian , Chi Fangli , Fan Dawei , Ma Maining , Zhou Wenge 

TITLE=Stability and Thermoelasticity of Diaspore by Synchrotron X-ray Diffraction and Raman Spectroscopy

JOURNAL=Frontiers in Earth Science

VOLUME=9

YEAR=2021

URL=https://www.frontiersin.org/journals/earth-science/articles/10.3389/feart.2021.752566

DOI=10.3389/feart.2021.752566

ISSN=2296-6463

ABSTRACT=<p>The thermoelasticity and stability of diaspore (α-AlOOH, Al<sub>1.002</sub>Fe<sub>0.003</sub>OOH) were investigated in this study by <italic>in situ</italic> 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 (<italic>P</italic>-<italic>T</italic>) 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 <italic>in situ</italic> high-pressure XRD experiments were fitted by the third-order Birch-Murnaghan equation of state (EoS) with the zero-pressure unit-cell volume <italic>V</italic><sub>0</sub> = 118.15 (4) Å<sup>3</sup>, the zero-pressure bulk modulus <italic>K</italic><sub>V0</sub> = 153 (2) GPa, and its pressure derivative <italic>K</italic>'<sub>V0</sub> = 2.4 (3). When <italic>K</italic>'<sub>V0</sub> was fixed at 4, the obtained <italic>K</italic><sub>V0</sub> = 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 <italic>K</italic><sub>a0</sub> = 137 (5) GPa, <italic>K</italic><sub>b0</sub> = 169 (7) GPa and <italic>K</italic><sub>c0</sub> = 178 (6) GPa. In addition, the temperature-volume data from <italic>in situ</italic> high-temperature XRD experiments were fitted by Fei’s thermal equation with the thermal expansion coefficients <italic>α</italic><sub><italic>V</italic></sub> = 2.7 (2) × 10<sup>–5</sup> K<sup>−1</sup>, <italic>α</italic><sub><italic>a</italic></sub> = 1.13 (9) × 10<sup>–5</sup> K<sup>−1</sup>, <italic>α</italic><sub><italic>b</italic></sub> = 0.77 (5) × 10<sup>–5</sup> K<sup>−1</sup>, and <italic>α</italic><sub><italic>c</italic></sub> = 0.85 (9) × 10<sup>–5</sup> K<sup>−1</sup> for diaspore, which shows that diaspore exhibits slightly anisotropic thermal expansion. Furthermore, <italic>in situ</italic> synchrotron-based single-crystal XRD under simultaneously high <italic>P</italic>-<italic>T</italic> conditions indicates that the <italic>P</italic>-<italic>T</italic> 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.</p>