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

Abstract

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 (Rcl) were determined to be in the range 40 to 190 nm and the volumes of the defect clusters (Acl) 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.