Seminár z fyziky kondenzovaných látok - Roman Martoňák (8.10.2026)

vo štvrtok 8.10.2026 o 14:00 v posluchárni F1 108

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Prednášajúci: prof. Ing. Roman Martoňák, DrSc.

Názov: What is there beyond diamond?

Termín: 8.10.2026, 14:00 hod., F1/108

Abstrakt:
Diamond is exceptional for many reasons. Besides being the hardest material found in Nature (and likely also among the most beautiful ones), it also has an extremely wide region of stability in pressure. Persisting at ambient conditions as metastable phase on geological time scales, and becoming thermodynamically stable already at relatively low pressure of about 1.6 GPa (16 kbar), it has never been observed to transform to another phase upon compression. The question of what is beyond diamond is of interest for several decades. As early as 1984, it was theoretically predicted that the cubic diamond phase of carbon is thermodynamically stable up to 1 TPa (10 Mbar), three times higher than the pressure in the Earth's centre. The next phase following diamond in the phase diagram was predicted to be the BC8 phase, well known as a metastable phase in silicon. However, no transformation of diamond was observed in ramp compression experiments where the pressure reached even 2 TPa. The observation of post-diamond phases in carbon thus represents one of the open problems of high-pressure physics. In my talk I will review the past and current experimental attempts aiming at synthesis of BC8 and present theoretical efforts in this field. I will then show our recent results of simulations of structural transformations at TPa pressures based on metadynamics and machine learning potentials. These reveal atomistic details of possible formation of BC8 upon compression and decompression and also address the question of its possible stability upon quenching to ambient conditions.

 

 

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