Stresses generated by impurities in diamond

Single dissolved nitrogen, boron or hydrogen atoms cause the diamond lattice around them to expand by 40%, 33.7% and 31%, respectively. Such large atomic strains generate short-range stresses around each dissolved impurity atom. If the impurity is dissolved uniformly in a diamond crystal, the atomic strains around each impurity atom will produce an overall uniform expansion that will not generate macro stresses in the diamond crystal. However, if the impurity is not dissolved uniformly, incompatible macrostrains will result that will generate large elastic stresses in the diamond crystal. These stresses may strengthen or weaken a diamond crystal depending on their magnitudes, signs (i.e. compression or tension) and spatial distributions in the crystal. An inhomogeneous distribution of impurities can be generated either by the appearance of higher order growth facets during crystal growth, which generate differential segregation of impurities between the high- and low-order crystal growth sectors or by temporal changes in growth conditions which generate radial impurity gradients. Since growth conditions control the distribution of impurities in the diamond, diamonds can be strengthened or weakened by different growth conditions.