Structural peculiarities of carbon onions, formed by four different methods: Onions and diamonds, alternative products of graphite high-pressure treatment

We attempted to find peculiarities of the carbon onion structure specific to onions synthesized by four different methods, three of them using high-pressure techniques, and to explain the lack of diamond particles. Within the framework of the theory of shell deformation, it was shown that the formation of diamond particles from onions requires the application of a much higher external pressure and the production of onions represents a dead-end branch of high-pressure graphite–diamond transformations.