X-ray topographic images of several dozens of diamonds were recorded before and after their use as anvils in a diamond anvil high pressure cell. The aim of this study was to better understand and prevent the breakage of diamond anvils when they were used in contact with a helium sample. Indeed, helium was a good hydrostatic medium for very high pressure studies but many anvils were subjected to helium embrittlement. X-ray topographic observations suggested that helium atoms enter the diamond anvil by a diffusion process enhanced by subsurface strains and/or extended pre-existing defects and non-hydrostatic stress. Then these atoms open cracks during non-hydrostatic load of the diamond anvil. The diamond anvils could be classified into three types depending on the nature of the defects. An associated criterion for the selection of stones resistant to helium was proposed.

An X-ray Topographic Study of Diamond Anvils: Correlation between Defects and Helium Diffusion. Dewaele, A., Loubeyre, P., Andŕ, R., Härtwig, J.: Journal of Applied Physics, 2006, 99[10], 104906