Old Story New Tell: The Graphite to Diamond Transition Revisited

Graphite and diamond are two well-known allotropes of carbon with distinct physical properties due to different atomic connectivity. Graphite has a layered structure in which the honeycomb carbon sheets can easily glide, while atoms in diamond are strongly bonded in all three dimensions. The transition from graphite to diamond has been a central subject in physical science. One way to turn graphite into diamond is to apply the high pressure and high temperature (HPHT) conditions. However, atomistic mechanism of this transition is still under debate. From a series of large-scale molecular dynamics (MD) simulations, we report a mechanism that the diamond nuclei originate at the graphite grain boundaries and propagate in two preferred directions. In addition to the widely accepted [001] direction, we found that the growth along [120] direction of graphite is even faster. In this scenario, cubic diamond (CD) is the kinetically favorable product, while hexagonal diamond (HD) would appear as minor amounts of twinning structures in two main growth directions. Following the crystallographic orientation relationship, the coherent interface t-(100)gr//(11-1)cd + [010]gr//[1-10]cd was also confirmed by high-resolution transmission electron microscopy (HR-TEM) experiment. The proposed phase transition mechanism does not only reconcile the longstanding debate regarding the role of HD in graphite-diamond transition, but also yields the atomistic insight into microstructure engineering via controlled solid phase transition.

Keywords: Phase transition, molecular dynamics simulation, super hard materials

Suggested Citation: Suggested Citation

Zhu, Shengcai and Yan, Xiaozhi and Liu, Jin and Oganov, Artem and Zhu, Qiang, Old Story New Tell: The Graphite to Diamond Transition Revisited. Available at SSRN: https://ssrn.com/abstract=3565046 or http://dx.doi.org/10.2139/ssrn.3565046

This version of the paper has not been formally peer reviewed.