Three large (4–7 mm) natural diamonds, each half brown and half white, from the Argyle Diamond Mine in Western Australia, have been studied for growth history and crystal perfection. Scanning electron microscopy and X‐ray single‐crystal topography showed the diamonds to have good octahedral morphologies but poor internal perfection. X‐ray double‐crystal topography quantified this lack of perfection, rocking‐curve widths taking unusually large values of 300 and 75 s of arc for the brown and white regions, respectively, in a diffraction geometry for which 3 s of arc would be expected for a perfect diamond. Fourier transform infrared spectroscopy revealed significant differences in nitrogen concentration between the brown and white regions of the diamonds. The white regions, with 400 to 600 p.p.m. nitrogen, contained over 1.6 times more nitrogen than the brown regions. It is concluded that the extra nitrogen (in A and B forms) in the white regions stiffens the lattice against distortion by natural plastic deformation.
Abstract:The characterization of growth features and defects in various high-pressure high-temperature (HPHT) synthetic diamonds has been achieved with optical and X-ray topographic techniques. For the X-ray studies, both characteristic and synchrotron radiation were used. The defects include dislocations, stacking faults, growth banding, growth sector boundaries, and metal inclusions. The directions of the Burgers vectors of many dislocations (edge, screw, and mixed 30˝, 60˝, and 73.2˝), and the fault vectors of stacking faults, were determined as <110> and 1/3 <111> respectively. Some dislocations were generated at metallic inclusions; and some dislocations split with the formation of stacking faults.
Surface morphology, individual grains and cracks in free-standing polycrystalline diamond samples have been imaged by a series of x-ray phase-contrast techniques, using well collimated synchrotron radiation of moderate coherence length at a `second-generation' source (Daresbury, UK). Whole samples (10 × 10 mm2 and larger) as well as selected regions have been studied. These contained crystallites of diameters in the range 50-200 µm. Contrast control has been achieved by varying the angle of an analysing crystal in the transmitted beam.
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