The size dependence of the diamond-graphite transition

The transition between nanometre-scaled diamond and graphite as well as the corresponding thermodynamic functions are discussed based on the temperature-pressure phase diagram of carbon including the contribution due to surface effects. As a result, the equilibrium transition size between diamond and graphite as a function of temperature and the thermodynamic function for the transition are obtained. It is found that as the size and temperature decrease, diamond becomes more stable than graphite. The obtained result is consistent with the reported experimental results on the chemical vapour synthesis of nanometre-sized diamond under ambient pressure.