Atomistic Evidence of Carbon Allotropes Recovered from High-pressure and High-Temperatures

It is of importance to form new carbon allotropes as well as understand the transformation mechanism from graphite to diamond. Extensive theoretical studies have been carried out including the prediction of several tens of new forms of carbon allotropes using machine learning, and the understanding of the direct graphite to diamond nucleation mechanism using quality neural-network potential. Here we bridge the gap between the simulation predictions and experimental observations using aberration corrected TEM. First, we report the observation of hexagonal and cubic diamonds with a diaphite structure, which has both diamond-like and graphite-like bond lengths. We will also show atomic observations of the direct transformation pathway from graphite to diamond through an intermediate metastable graphite phase. Overall, the creation of the new carbon forms clues that under modulated high pressure and temperature conditions, the great diversity of carbon covalent bonds could be assembled into carbon allotropes.