To obtain exotic forms of carbon, scientists squeezed the diamond with record force, but it retained its structure even at the maximum pressure that was achieved.
Carbon is perhaps the most "multifaceted" of the elements. Depending on the conditions, it can be in the form of graphene, graphite, and at very high pressure and temperature it forms superhard diamond. It is believed that diamond structures appear not only in the bowels of the Earth, but also on other planets, and as pressure increases, they can transform into other, exotic forms of carbon.
To investigate these unusual structures, American scientists created the right conditions in the laboratory. Amy Lazicki and her colleagues at Livermore National Laboratory and the University of Washington compressed diamond samples to 2 TPa (20 million atmospheres) - twice as strong as the previous record achieved in the laboratory and five times as strong as at the Earth's core.
"This is the highest pressure at which it was possible to measure the properties of the crystal lattice," says one of the scientists, "determining the key parameters of strength, melting and chemical bonds for carbon." Microscopic samples were compressed by high-power laser pulses, while simultaneously taking X-ray diffraction images on these structures with nanosecond time resolution. The results of the work are presented in an article published in the journal Nature.
Much to the surprise of scientists, the "stability limits" of a diamond, beyond which it must go into other unusual structures, have not been reached. The crystal lattice remained stable even at the new record pressure. “This phase of carbon has proven to be the most stable structure known,” says Ryan Rygg, another author of the paper.
According to Rigg, the findings are changing our understanding of the behavior of carbon in the bowels of the planets, where diamonds are deposited: "Now we think that diamond structures are preserved in a much wider range than previously thought." If new exotic forms of carbon are indeed formed, they require very harsh conditions that are not found everywhere. On the other hand, this increases the chances of the existence of hypothetical planets consisting of almost entirely diamond.