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Diamonds can take a little bit of pressure. Actually, review this – diamonds can take a lot of pressure. In a series of new experiments, scientists have found that diamonds retain their crystal structure at pressures five times higher than those in the Earth’s core.
This contradicts predictions that the diamond would have to transform into an even more stable structure under extremely high pressure, suggesting that the diamond adheres to one shape under conditions where another structure is more stable, which is called “Metastable”.
This discovery has implications for the modeling of high pressure environments such as the cores of carbon-rich planets.
Carbon is about as common as it gets. It is the fourth most abundant element in the Universe, and can be found in exoplanets and stars and the space in between. It is also a main ingredient of all known life on Earth. Without it, we wouldn’t exist; that’s why we call ourselves a carbon-based life.
Thus, carbon is of intense interest to scientists of all kinds. However, one place where carbon can be found – the nuclei of carbon-rich exoplanets – is very difficult to study. The high pressures present therein are difficult to reproduce, and once the high pressures are reached, the compressed material is difficult to probe.
We know that carbon has several allotropes, or variant structures, at ambient pressures that have significantly different physical properties. Charcoal, graphite, and diamond all form at different pressures, with diamond occurring at higher pressures deep underground, starting at around 5 or 6 gigapascals.
The pressure at the heart of the Earth is about 360 gigapascals. At even higher pressures – around 1000 gigapascals, just over 2.5 times the central pressure of Earth, scientists predicted that carbon would transform again into several new structures, structures we never have. seen or made before.
One method of achieving incredibly high pressures involves the use of a diamond anvil and shock compression. With this method, the hydrocarbon was subjected to 45,000 gigapascals. This method tends to destroy the sample before its structure can be probed.
A team led by physicist Amy Lazicki Jenei from Lawrence Livermore National Laboratory has found another way to make it work. They used ramp-shaped laser pulses to squeeze a solid carbon sample, at a pressure of 2000 gigapascals. Simultaneously, time resolved X-ray diffraction of nanosecond duration was used to probe the crystal structure of the sample.
This more than doubled the previous pressure at which a material was probed using x-ray diffraction. And the results surprised the team.
“We have found that, surprisingly, under these conditions, the carbon does not transform in any of the expected phases but retains the structure of the diamond up to the highest pressure,” Jenei said.
“The same ultra-strong interatomic bonds (requiring high energies to break), which are responsible for the metastable diamond structure of carbon which persists indefinitely at room pressure, also probably prevent its transformation above 1000 gigapascals in our experiments. .
In other words, diamond does not expand into graphite when it comes out of the deep subsoil: from higher pressures to lower pressures. The force that prevents this reversion could explain why the diamond does not reorganize into another allotrope at pressures even higher than those in which it formed.
The discovery could change the way scientists model and analyze carbon-rich exoplanets, including the mythical diamond planets.
In the meantime, there is still work to be done to understand the result. The team isn’t quite sure why diamond is so strong – more research will be needed to understand why diamond is metastable over a wide range of pressures.
“Whether nature has found a way to overcome the high-energy barrier to the formation of predicted phases inside exoplanets is still an open question,” Jenei said.
“Further measurements using an alternative compression pathway or from an allotrope of carbon with an atomic structure that requires less energy to reorganize will provide additional information.”
The research was published in Nature.
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