Diamonds can handle some stress. In fact, revisit that – diamonds can handle a lot of stress. In a series of new experiments, scientists have discovered that diamonds maintain their crystal structure at weights five times higher than the Earth’s core structure.
This contradicts the prediction that diamonds should transform into an even more stable structure under very high pressure, suggesting that diamonds retain shape under conditions where another structure would be more stable, which is called ‘metastable’.
This discovery has had an impact on shaping high-pressure environments such as the hearts of carbon-rich planets.
Carbon is almost as common as it gets. It is the fourth most abundant element in the Universe, and is found in exoplanets and stars and the space between them. It is also the main ingredient of all known life on Earth. Without it, we would not exist; that is why we refer to ourselves as a carbon – based life.
So carbon is of great interest to scientists of all kinds. However, it is very difficult to study one place where carbon is found – the hearts of carbon – rich exoplanets. The high pressures present are difficult to reproduce and, once large pressures are achieved, the compressed material is difficult to study.
We know that carbon has a number of allotropes, or variable structures, at environmental pressures that have very different physical properties. Charcoal, graphite and diamonds all come under different pressures, with diamonds appearing at higher pressures deep underground, starting at about 5 or 6 gigapascals.
The weight at the heart of the Earth is up to about 360 gigapascals. At even higher weights – around 1,000 gigapascals, just over 2.5 times the Earth’s core weight, scientists have predicted that carbon would transform into a number of new structures, some of which we have not seen. or that we have never achieved before.
One way to achieve high gelatinous weights involves the use of diamond anvils and shock absorbers. With this method, 45,000 gigapascals were delivered hydrocarbon. That method tends to destroy the sample before its structure is determined.
A team led by physicist Amy Lazicki Jenei of Lawrence Livermore National Laboratory found another way to make it work. They used ramp-shaped laser beats to crush a solid carbon sample, to a weight of 2,000 gigapascals. At the same time, a nanosecond time-adjusted X-ray differential was used to study the crystal structure of the sample.
This doubled the previous weight at which material was determined using X-ray differentiation. And the results surprised the team.
“We found that, surprisingly, under these conditions carbon does not change to any of the expected levels but maintains the structure of the diamond up to its maximum weight,” Jenei said.
“The same ultra-strong intermediate bonds (which require high breaking energy), which rely on a metastable diamond structure of carbon to survive indefinitely at environmental pressures, also impede transformed over 1,000 gigapascals in our tests. “
In other words, diamonds do not rest back to graphite when extracted from depths underground: from higher to lower weights. The strength that prevents that reversal is why diamonds do not recombine to another allotrope at pressures even higher than those in which it formed.
This discovery could change how scientists model and study carbon-rich exoplanets, including the mythical diamond planets.
At the same time, more work needs to be done to understand the outcome. The team is not entirely sure why diamonds are so strong – more research will be needed to find out why diamonds are metastable over a wide range of weights.
“Whether nature has found a way to overcome the high energy barrier in creating the projected levels within exoplanets remains an open question,” Jenei said.
“Further measurement by using an alternative condensation pathway or starting from an allotrope of carbon with an atomic structure that requires less energy to redistribute will provide more insight.”
The research was published in Nature.