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 (r ho) measurements, topography and diffuse X-ray scattering (DXS) techni ques are reported. The samples are [111] natural diamond platelets of dimensions similar to 2 x 2 mm with thickness in the range similar to 0.5-1 mm. A five-crystal X-ray diffractometer in three-crystal configu ration as well as a four-crystal diffractometer were employed with Mo K alpha(1) as the exploring radiation. Infrared absorption measurement s showed that the samples belong to type Ia variety and contained vary ing concentrations of A and B forms of nitrogen aggregates as well as platelets. There were large variations in the values of diffraction cu rve half-widths (18 to 550 '') and values of rho (2.4 x 10(-5)-76 x 10 (-5) rad) for 111 reflection, showing a wide variation in crystalline perfection. Projection and composite stationary X-ray topographs recor ded with different diffraction vectors showed the presence of defects like low-angle boundaries. From the analysis of the observed distribut ion of diffuse X-ray scattering (DXS), point defect clusters were char acterized. The clusters were of interstitial as well as vacancy type. The sizes of the defect clusters (R-cl) were determined to be in the r ange 40 to 190 nm and the volumes of the defect clusters (A(cl)) were in the range similar to 1 x 10(-25)-28 x 10(-25) m(3). The defect clus ters with sizes reported here could be investigated as the measurement s were made close to the reciprocal-lattice points. The platelet size was found to vary inversely with the total concentration of nitrogen.