Study of Structural Imperfections in Natural Type I Diamonds by High-Resolution X-ray Diffraction Techniques

Results of characterization of defects in natural diamond crystals by high-resolution X-ray diffractometry, absolute integrated intensity (ρ) measurements, topography and diffuse X-ray scattering (DXS) techniques are reported. The samples are 〈111〉 natural diamond platelets of dimensions ~2 × 2 mm with thickness in the range ~0.5–1 mm. A five-crystal X-ray diffractometer in three-crystal configuration as well as a four-crystal diffractometer were employed with Mo Kα₁ as the exploring radiation. Infrared absorption measurements showed that the samples belong to type Ia variety and contained varying concentrations of A and B forms of nitrogen aggregates as well as platelets. There were large variations in the values of diffraction curve half-widths (18 to 550′′) and values of ρ (2.4 × 10⁻⁵–76 × 10⁻⁵ rad) for 111 reflection, showing a wide variation in crystalline perfection. Projection and composite stationary X-ray topographs recorded with different diffraction vectors showed the presence of defects like low-angle boundaries. From the analysis of the observed distribution of diffuse X-ray scattering (DXS), point defect clusters were characterized. The clusters were of interstitial as well as vacancy type. The sizes of the defect clusters (R_cl) were determined to be in the range 40 to 190 nm and the volumes of the defect clusters (A_cl) were in the range ~1 × 10⁻²⁵–28 × 10⁻²⁵ m³. The defect clusters with sizes reported here could be investigated as the measurements were made close to the reciprocal-lattice points. The platelet size was found to vary inversely with the total concentration of nitrogen.