The nanoscale hexagonal diamond
In a first in physics, Chinese scientists created small pure samples of the elusive mineral lonsdaleite (known as hexagonal diamond) and tested its material properties to show that it is harder than natural diamond.
A group of researchers from Zhengzhou University (China) have produced what they claim to be the first samples of pure hexagonal diamond – a rare and theorized variant of super-strong diamond found in meteorites from destroyed dwarf planets.
O Natural diamond is considered the hardest natural material on Earth for so long that the Mohs hardness scale (which classifies minerals’ resistance to scratching) uses diamond as the upper limit of the scale.
It is also called cubic diamond due to its ordered arrangement of carbon atoms in a cubic structure.
In contrast, the diamante hexagonal organizes carbon atoms into a network formed by hexagons, like a honeycomb.
As , in 1962, scientists from the Pittsburg Coal Research Center (USA) theorized that the layers of carbon atoms that make up diamond could be organized into a hexagonal network instead of a cubic one, thanks to the way carbon forms bonds with other carbon atoms.
In 1967, researchers discovered hexagonal diamond — or lonsdaleíte — in the laboratory, suspecting that it might be harder than cubic diamond.
They began looking for it in a special type of diamond-rich meteorite called ureilitowhich forms from the mantle of destroyed dwarf planets.
The first detections of hexagonal diamonds in nature were documented in a 1967 article, recalls the same magazine.
The biggest challenge in identifying lonsdaleitis is the lack of pure samples. In many cases, it is mixed with cubic diamond, graphite and other minerals. This makes it difficult (or even impossible) to test and measure their unique properties.
The new study, earlier this month in Natureaddressed this problem by creating several pure hexagonal diamond samples about 1.5 millimeters in diameter — large enough to measure the samples’ material properties.
As reported by Live Science, the team discovered that the hexagonal diamond is simultaneously stiffer and harder than cubic diamondand that resists oxidation much better than cubic diamond.
This means that hexagonal diamond can tolerate much higher temperatures without its surface becoming covered in residue due to reaction with oxygen, which is important for applications such as drilling.
To produce the samples, the researchers compressed very organized graphite (graphite with regularly ordered carbon atoms) for 10 hours at 20 gigapascals, or about 200,000 times Earth’s atmospheric pressure at sea level, and subjected it to temperatures between 1,300 to 1,900 degrees Celsius.
At higher temperatures and pressures, lonsdaleite began to transform into cubic diamond.
“The elusive material has potential applications in many fields, for example in cutting tools, thermal management materials and quantum sensing,” he said. Chong-Xin Shanleader of the study, Nature in another
