Carbon is not only the fourth most abundant element in the universe, but it is the building block of all known life forms, and it is also found in the interior of carbon-rich outer planets. Therefore, it is receiving great attention by scientists.
And carbon has peculiar properties. On their own, they can form graphite that is abundant and less hard, or diamonds that are rarely very hard. This is due to the ability of carbon atoms to bond with each other and arrange themselves into different crystalline shapes, each of which has its own distinctive physical properties. It is a phenomenon known as allotropy.
However, the arrangement of carbon atoms in this or that way is subject to the influence of external factors, such as pressure and temperature. Graphite and diamond are formed at different pressures; Whereas graphite is formed under local pressure conditions, diamonds are formed at a pressure of 5 to 6 gigapascals underground.
In addition, scientists have speculated that there are many crystalline structures that carbon could take, which would form at a pressure of more than a thousand gigapascals, which is 2.5 times more than the pressure in the Earth’s core.
The earlier projections were the product of exoplanet modeling processes, which were not verified in the laboratory. Scientists also previously believed that the structure of diamonds is subject to a semi-stable state, which soon turns into a more stable state under conditions of very high pressure.
However, it is difficult to reach that very high pressure except in the interior of the carbon-rich outer planets, which makes it very difficult to study, and even if we were able to reach a high pressure, it is difficult to examine the material under its influence.
In a recent study published in Nature on January 27, scientists at the Nation Ignition Facility of Lawrence Livermore National Laboratory and the University of Oxford discovered Oxford); Diamond maintains its crystal structure at pressures 5 times greater than those found in the Earth’s interior.
Thus, these results contradict private expectations that diamonds will transform into a more stable structure under the influence of very high pressure.
Although some previous laboratory methods were able to reach high pressures, they caused destruction of the sample before examining its crystal structure. The team, led by Amy Laziki Jeni, overcame this obstacle by using pulses of the glide laser to create a pressure of 2,000 gigapascals on a sample of solid carbon. At the same time, the scientists examined the sample’s crystal structure, using time-spaced X-ray diffraction in a range of nanoseconds.
According to the press release published by Lawrence Livermore National Laboratory, Jenny commented on the findings, saying that “carbon does not transform into any of the most stable states that were previously formulated, but it does preserve the diamond crystal structure even under the highest pressure we can reach.”
Jenny attributes this to “the super-strong bonds that link the atoms, which require great energy to break them. This gives carbon the diamond structure that enables it to remain for long under ambient pressures, as well as resist its transformation at a pressure exceeding a thousand gigapascals in our experiments.”
And because the carbon atoms in diamonds do not rearrange themselves to take the shape of graphite once they emerge from the Earth’s core where the high pressure is, this may be the same reason that prevents them from rearranging themselves into another “allotropic” shape if they encounter a higher amount of pressure on them. However, we still need more research to know the reason behind the stability of diamonds at different pressures.
Of course, there remains an open question, says Jenny, which is: “Has nature created a mechanism to overcome the high energy barrier to be able to form the stable stages previously expected in the interior of the outer planets?”
Until we can answer this question, this discovery will undoubtedly change how scientists model and analyze carbon-rich exoplanets.