[S-CG62] Rheology, fracture and friction in Earth and planetary sciences

[SCG62-P07] Investigation of Microstructural Observation and Crystal Preferred Orientation Analysis in rDAC Deformed Samples Using XRD and EBSD

*Bunrin Natsui¹, Shintaro Azuma¹, Masahiro Yasutake², Yukinojo Koyama³, Keishi Okazaki^4,5, Kentaro Uesugi², Saori Kawaguchi², Ryuichi Nomura⁶, Kenji Ohta¹ (1.Institute of Science Tokyo, 2.Japan Synchrotron Radiation Research Institute, 3.The University of Tokyo, 4.Hiroshima University, 5.Japan Marine Science and Technology Center, 6.Kyoto University)

Keywords:Lower mantle, Ferropericlase, Deformation Experiment, X-ray diffraction, Crystallographic preferred orientation , Electron Backscatter Diffraction

The rotational diamond anvil cell (rDAC) is a device capable of performing deformation experiments under the full pressure conditions of Earth's interior. In recent years, results from high-temperature and high-pressure deformation experiments on minerals using rDAC have been reported. Deformation experiments using rDAC are commonly performed in combination with synchrotron X-rays at SPring-8. To date, the determination of crystallographic preferred orientation (CPO) in rDAC experiments has been performed using X-ray diffraction (XRD) measurements. However, there are several limitations in measuring CPO during deformation experiments with XRD. For example, in the experimental setup of rDAC, XRD data can only be obtained from a single direction, and the sample during deformation is tilted by 60 degrees relative to the rotational axis. As a result, only a limited range of pole figures corresponding to the 60-degree tilt can be obtained. The overall pole figure (covering a 180-degree range) is reconstructed based on this limited data range, but the completeness of the reconstructed data has not been thoroughly verified. Furthermore, X-ray measurements do not allow for detailed evaluation of individual crystallites, such as grain size and particle shape in polycrystalline samples.
In this study, we performed XRD and electron backscatter diffraction (EBSD) measurements on samples after pressure decompression, which had undergone in-situ XRD measurements during rDAC torsional deformation experiments. The microstructural observation and CPO determination of FeO and (Mg,Fe)O samples were carried out, and the obtained CPO was compared with that determined from XRD measurements before and after pressure decompression. The CPO determination of the deformed samples was attempted using XRD data obtained at a single angle (60 degrees relative to the rotation axis). For CPO analysis, the Rietveld analysis incorporating the crystallite orientation distribution function (ODF) in the Material Analysis Using Diffraction (MAUD) software was applied. Additionally, after deformation, the samples were recovered by decompression, and multi-angle (-35 degrees to 35 degrees) XRD measurements were conducted at SPring-8 BL10XU to determine the CPO.
The obtained CPOs were consistent between the samples after deformation (BL47XU data) and those after decompression recovery (BL10XU data), confirming that the effect of deformation during decompression on CPO was minimal. Deformation experiments were performed on (Mg, Fe)O at pressures of 0-126 GPa, temperatures of 300-950 K, and constant strain rates. Furthermore, for some decompression-recovered samples, EBSD measurements were performed on samples prepared by focused ion beam (FIB) polishing to analyze microstructure and CPO. The results showed that the CPO of FeO was generally consistent with the XRD results. Additionally, EBSD mapping revealed a continuous change in crystal orientation within the same grain, suggesting that the sample deformed by dislocation creep during the deformation experiment.