Three-dimensional X-ray topographic characterization of broken and unbroken natural diamond anvil crystals at 99.4 GPa

その他

Three-dimensional (3D) X-ray topography was used to characterize diamond anvil crystals before and after application of ultra-high pressure at 50, 70 and 99.4 GPa. The diffraction planes examined and the wavelength of the monochromatic X-rays were (004), (333), {224}, {440} and 0.0521 nm, respectively. Images of lattice defects in the diamond crystals were reconstructed by stacking approximately 500 X-ray limited projection topographs using the image processing software Image J. The 3D structures and nature of the lattice defects were identified from the reconstructed topographs. A pyramidal shape of four parts of stacking faults was identified using the visibility or invisibility of defect images with each diffraction plane. No significant changes of the lattice defects in the diamond crystals were observed under pressurization at 70 GPa. However, one of the anvil crystals shaped from the same rough crystal was broken into pieces at 99.4 GPa. The fracture stress is very low value rather than the calculated one based on (111) [110] slip system mechanism. In the broken crystal, the center line of plurality of the pyramidal shape of stacking faults differed in the location from the culet area. The breaking of diamond crystal was dependent on the distribution of plane defects in the crystal.