On the role of nitrogen in stiffening the diamond structure

Abstract

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.