Melting diamond in the diamond cell by laser-flash heating

ABSTRACT

The phase behavior of carbon at high pressure and the search for carbon structures denser than diamond has been explored for decades showing large discrepancies, with many fundamental questions remaining unresolved. Here we show evidence of melting above the graphite-diamond-liquid (GDL) triple point (∼13 GPa, 4000 K) up to 50 GPa on samples recovered from single flash-heating events using spectroscopic and electron microscopic methods. The results show that for all pressures, diamond melts below the triple point temperature contradicting previous studies, most of which predict a positive slope of the melting curve.

KEYWORDS:

• Diamond cell
• laser-heating
• diamond melting

Acknowledgements

We thank C. Zhang for his help in the SEM operation and M. Somayazulu for his help with the Raman measurements, both at the Earth and Planets Laboratory, DC, USA. The authors gratefully acknowledge the scientific and technical assistance of the RMIT Microscopy & Microanalysis Facility, a linked laboratory of the Microscopy Australia.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported as part of Energy Frontier Research in Extreme Environments Center (EFree), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001057. BH and RB used resources at the High Flux Isotope Reactor and the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. D.G.M., B.H., R.B. and J.E.B would like to acknowledge the support from the Australian Research Council (ARC) Discovery Project scheme (DP170102087 and DP190101438).