Carbon comes in many different structures, most famously graphite and diamond. Other forms were predicted to exist at extremely high pressures, but now researchers have examined carbon under the highest pressure ever studied in the lab, and found that diamond sticks around much longer than expected.
One of the most abundant elements in the universe, carbon is the basis for all known life and much of the Earth itself. It takes on many different forms under different circumstances – the high pressures and temperatures deep inside the planet turn it into diamond. Other, more exotic structures were expected to exist at even higher pressures, above 1,000 gigapascals (GPa).
So, in a new study, a team of scientists put the squeeze on carbon far above that pressure to find out what those other forms might be. The researchers compressed solid carbon to 2,000 GPa, which is five times higher than the pressure in the Earth’s core and twice as high as the previous record pressure under which carbon has been studied in the lab.
“This is the highest pressure any atomic structure has been measured (at), placing key constraints on the equation of state, material strength, melting, and chemical bonding of carbon,” says Gilbert Collins, co-author of the study.
The team used ramp-shaped laser pulses to compress the carbon, and took nanosecond-long images of its crystal structure using an X-ray diffraction platform.
Surprisingly, the researchers found that carbon kept its diamond structure for much longer than expected. Rather than converting into other forms, it seems that diamond’s molecular bonds are far more stable than the mineral was previously given credit for.
“The diamond phase of carbon appears to be the most stubborn structure ever explored,” says Ryan Rygg, co-author of the study. “This could have implications for carbon in the deep interiors of planets, where the precipitation of diamond is expected. Now we anticipate the diamond structure of carbon will persist over a much greater range of planetary conditions than we previously thought.”
This could mean that some of the theoretical forms of carbon might not exist, or at least only develop under even greater pressures or different circumstances. It may also suggest that “diamond planets” are more common out in the cosmos than we thought.
The research was published in the journal Nature.
Source: University of Rochester
