Asteroid impacts create diamond materials with exceptionally complex structures

19-07-2022

Shockwaves caused by asteroids colliding with Earth create materials with a range of complex carbon structures, which could be used for advancing future engineering applications, according to an international study led by UCL and Hungarian scientists, involving the ESRF ID27 beamline.

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Diamond is the hardest material found in nature. Its applications range from abrasives and electronics to nanomedicine and laser technology. Understanding its structure and properties is of key importance. The common form of diamond is cubic. Yet, dense carbon materials formed by shock compression have been described as hexagonal diamond or lonsdaleite.  In a study published in Proceedings of the National Academy of Sciences, the team of researchers found that diamonds formed during a high-energy shock wave from an asteroid collision around 50,000 years ago have unique and exceptional properties, caused by the short-term high temperatures and extreme pressure. They provide a structural understanding of lonsdaleite and demonstrates the existence of bulkmaterials containing extensive regions of nanostructured diamond and graphene-like intergrowths called diaphites.

3D_diaphite_colour.jpg

Diaphite (diamond-graphite) structure created during asteroid impact. The central part outlined with the red diamond symbol (~ 1.5 nm) represents nanocrystalline diamond, and the green color represents graphite. The transition color between red and green refers to the transition bond type of diamond and graphite.

The researchers say that these structures can be targeted for advanced mechanical and electronic applications, giving us the ability to design materials that are not only ultra-hard but also malleable with tunable electronic properties.

For the study, the international team of scientists used detailed state-of-the-art crystallographic and spectroscopic examinations of the mineral lonsdaleite from the Canyon Diablo iron meteorite first found in 1891 in the Arizona desert.

Named after the pioneering British crystallographer Professor Dame Kathleen Lonsdale, lonsdaleite was previously thought to consist of pure hexagonal diamond, distinguishing it from the classic cubic diamond. However, the team found that it is in fact comprised of nanostructured diamond and graphene-like intergrowths (where two minerals in a crystal grow together) called diaphites. The team also identified stacking faults, or “errors” in the sequences of the repeating patterns of layers of atoms. 

“Through the recognition of the various intergrowth types between graphene and diamond structures, we can get closer to understanding the pressure-temperature conditions that occur during asteroid impacts.” explains Dr Péter Németh, from the Institute for Geological and Geochemical Research, RCAES.

The team found that the distance between the graphene layers is unusual due to the unique environments of carbon atoms occurring at the interface between diamond and graphene. They also demonstrated that the diaphite structure is responsible for a previously unexplained spectroscopic feature.

“This is very exciting since we can now detect diaphite structures in diamond using a simple spectroscopic technique without the need for expensive and laborious electron microscopy.” says Professor Chris Howard, from UCL Physics & Astronomy, co-author of the study.

The experiment performed at ESRF ID27 high-pressure beamline was essential for understanding the structure of the Canyon Diablo diamond and to reveal its diaphite content. "The outstanding performance of ID27, in particular, the intense two-micron-size X-ray beam  permitted to identify the complex diamond structures and map their structural variability with unprecedented detail.” says lMohamed Mezouar, ESRF scientist in charge of the beamline.

According to the scientists, the structural units and the complexity reported in the lonsdaleite samples can occur in a wide range of other carbonaceous materials produced by shock and static compression or by deposition from the vapour phase.  

“Through the controlled layer growth of structures, it should be possible to design materials that are both ultra-hard and also ductile, as well as have adjustable electronic properties from a conductor to an insulator”, adds Professor Christoph Salzmann, from UCL Chemistry, co-author of the study. “The discovery has therefore opened the door to new carbon materials with exciting mechanical and electronic properties that may result in new applications ranging from abrasives and electronics to nanomedicine and laser technology.”

As well as drawing attention to the exceptional mechanical and electronic properties of the reported carbon structures, the scientists also challenge the current simplistic structural view of the mineral denoted as lonsdaleite. 

References

News article based on a text published by UCL https://www.ucl.ac.uk/news/2022/jul/asteroid-impacts-create-diamond-materials-exceptionally-complex-structures

DOI: https://doi.org/10.1073/pnas.2203672119

Top image: A swarm of asteroids facing the Milky Way © iStock / Alexandr_Zharikov