Supercritical fluid synthesis and structure of C96 zeolite-like carbon allotrope

DOI: 10.62564/M4-OP2238

Sergii Maloshtan¹, Oleksii Pokropyvnyi², Anatolii Smolyar<sup>2

1</sup>M.P. Semenenko Institute of Geochemistry, Mineralogy and Ore Formation of the NAS of Ukraine
²Frantsevich Institute for Problems of Materials Science National Academy of Science of Ukraine


Since the beginning of the 21st century, we have entered the era of carbon allotropes. Among this wide spectrum of carbon structures, only four allotropes of carbon with cubic symmetry are currently known. Two of them are the well-known diamond and fullerite. Others are «cubic graphite» and cubic C8. Their structures were proposed as LTA and SOD carbon zeolites, respectively. Other possible structures are only hypothetical. In this report the structure of «cubic graphite» is reinvestigated based on a new electron diffraction experiment and ab initio calculations of carbon zeolites from an available structure database. Carbon microcrystals associated with the «cubic graphite» phase were synthesized using the fluid synthesis method at a pressure of up to 200 MPa and a temperature of 500-700 oС from carbon black as a precursor. According to the results of experiments, methods of experimental electron and X-ray diffractions, as well as ab initio calculations, it is proved that the carbon phase is cubic with lattice parameters ~0.895 nm and space group Im-3m [1]. The crystal structure is proposed as carbon C96 zeolite with KFI topology consisting of 96 carbon atoms per unit cell with sp3 hybridization and sp3/sp2 bond types. This type of zeolite consists of eight 6-6 prisms as secondary building units with T-atoms as individual carbon atoms instead of SiO2 in true zeolites. The hybrid structure is more stable by 0.22 eV per atom. New phase has a density of 2.67 g/cm3 and a high hardness up to 10-20 GPa.

Keywords
supercritical fluid, carbon allotropes, zeolites, X-ray diffraction

Acknowledgments
Not provided

References
[1] S.М. Maloshtan, A.V. Pokropivny, A.S. Smolyar, V.O. Kuts, V.O. Barcholenko, A.M. Titenko, M. Czank, W. Depmeier, Supercritical fluid synthesis and structure of a new cubic C96 phase as carbon KFI zeolite with sp3/sp2 hybridization, Mineral. Journ. (Ukraine), 2024, V.24, No.2, https://doi.org/10.15407/mineraljournal.46.02.000