ABSTRACT
Natural (12C) diamond is the hardest material, with a hardness of 10 Mohs. The elastic constants of 13C diamond are ∼0.5% higher than the corresponding values of natural diamond. Diamond is four times harder than sapphire, which has a hardness of 9 Mohs. The tensile strength of diamond is the highest in the [100] crystal direction and the lowest in the [111] direction. The maximum tensile strengths have been calculated to be 225, 130, and 90 GPa in the [100], [110], and [111] directions, respectively. Compressive strengths of diamond have been calculated to be 223.1, 469.0, and 470.4 GPa in the [100], [110], and [111] directions, respectively. The compressive strength of diamond has been measured to be 160 GPa by Ruoff and Wanagel using a diamond tip of 2 mm radius on a flat diamond anvil. The elastic compliances s 11, s 12, and s 44 of diamond have been measured to be 0.9524, −0.0991, and 1.7331 TPa−1, respectively, by Grimsditch and Ramdas using Brillouin scattering. Young's modulus in the [111] direction has been determined to be 1163 GPa. The values of the elastic constants c 11, c 12, and c 44 have been determined to be 10.764 ± 0/002 × 1012, 1.252 ×1012, and 5.774 ± 0.014 × 1012 dyn/cm2 by Grimsditch and Ramdas.
