11:45 AM - 12:00 PM
[SCG49-04] Determination of the crystal structure of Earth’s constituent materials using in-house single-crystal X-ray diffraction measurements
Keywords:single-crystal X-ray diffraction measurements, diamond anvil cell, crystal structure, high-pressure experiments, crystal structure refinement, high-pressure minerals
The crystal structures of Earth’s constituent materials are fundamental information to understand the physical and chemical properties of the interior of the solid Earth. While X-ray diffraction (XRD) measurement is a widely used technique to determine the crystal structures of materials, the single-crystal XRD measurement is the most powerful tool for crystal structure refinement. Recent studies have discovered many new crystal structures likely stable in the Earth’s deep interior by the single-crystal XRD measurement in diamond inclusions, shock veins in meteorites, and the recovered samples of high-pressure experiments. Although conventional in-house single-crystal XRD measurements require relatively large crystals, recent apparatus can measure the single crystals with grain sizes as small as several tens of micrometers. In addition, the in-house single-crystal XRD measurements have a great advantage in terms of time limitation compared to the synchrotron measurements.
Here we performed ex-situ/in-situ single-crystal XRD measurements in the sample of high-pressure experiments using an advanced X-ray diffractometer (Bruker, D8 Venture). The X-ray is efficiently focused by combining the ImS3.0 microfocus radiation source and confocal multilayer mirrors (HELIOS Optic), so the S/N ratios are sufficiently good from small samples, even at low acceleration voltages. Mo target is used to generate relatively high-energy X-rays suitable for measuring oxide samples in a diamond anvil cell (DAC). We used a two-dimensional detector (PHOTON Ⅲ) as the detector and the software package APEX4 for data processing after the measurement. SHELXL, which is integrated into APEX4, was used for crystal structure refinement. In the ex-situ measurement, we have measured Fe-, Al-bearing bridgmanite, and Fe5O6 iron oxide synthesized in a multi-anvil cell. Results showed that required measurements were completed in the single crystals with grain sizes of several 10 µm. The crystal structure refinement was successfully completed to reach an R factor of ~ 0.02. In the in-situ measurements, we measured ZrSiO4 zircon under high pressure using Boehler-Almax type DAC with a wide aperture angle. Although the R factor was relatively higher than ex-situ measurements, crystal structure refinement succeeded under high pressure.
Based on the obtained crystal structure, we estimated the charges of atoms by the bond valence sum method. The charges of Fe were nearly +2 in the FeO6 trigonal prismatic site and were between +2 and +3 in the FeO6 octahedral site in Fe5O6. This result is consistent with a previous study, which suggested that the electrical conductivities of (FeO)m(Fe2O3)n iron oxides are dominated by continuous chains formed by FeO6 octahedra. The results of in-situ high-pressure single-crystal XRD indicated that the data quality is largely affected by the hydrostatic condition in the DAC sample and the precision of the sample position. In-house apparatus is effective for measurements with many samples since there is no time limitation compared to measurements at a synchrotron radiation facility. As a strong complement to the synchrotron facility, the advanced in-house single-crystal XRD measurement is expected to contribute to the studies in solid earth science via crystallographic analysis of the experimental, geological, and meteoritic samples.
Here we performed ex-situ/in-situ single-crystal XRD measurements in the sample of high-pressure experiments using an advanced X-ray diffractometer (Bruker, D8 Venture). The X-ray is efficiently focused by combining the ImS3.0 microfocus radiation source and confocal multilayer mirrors (HELIOS Optic), so the S/N ratios are sufficiently good from small samples, even at low acceleration voltages. Mo target is used to generate relatively high-energy X-rays suitable for measuring oxide samples in a diamond anvil cell (DAC). We used a two-dimensional detector (PHOTON Ⅲ) as the detector and the software package APEX4 for data processing after the measurement. SHELXL, which is integrated into APEX4, was used for crystal structure refinement. In the ex-situ measurement, we have measured Fe-, Al-bearing bridgmanite, and Fe5O6 iron oxide synthesized in a multi-anvil cell. Results showed that required measurements were completed in the single crystals with grain sizes of several 10 µm. The crystal structure refinement was successfully completed to reach an R factor of ~ 0.02. In the in-situ measurements, we measured ZrSiO4 zircon under high pressure using Boehler-Almax type DAC with a wide aperture angle. Although the R factor was relatively higher than ex-situ measurements, crystal structure refinement succeeded under high pressure.
Based on the obtained crystal structure, we estimated the charges of atoms by the bond valence sum method. The charges of Fe were nearly +2 in the FeO6 trigonal prismatic site and were between +2 and +3 in the FeO6 octahedral site in Fe5O6. This result is consistent with a previous study, which suggested that the electrical conductivities of (FeO)m(Fe2O3)n iron oxides are dominated by continuous chains formed by FeO6 octahedra. The results of in-situ high-pressure single-crystal XRD indicated that the data quality is largely affected by the hydrostatic condition in the DAC sample and the precision of the sample position. In-house apparatus is effective for measurements with many samples since there is no time limitation compared to measurements at a synchrotron radiation facility. As a strong complement to the synchrotron facility, the advanced in-house single-crystal XRD measurement is expected to contribute to the studies in solid earth science via crystallographic analysis of the experimental, geological, and meteoritic samples.