The staff of the ELKH Research Centre for Astronomy and Earth Sciences (CSFK) and the ELKH Centre for Energy Research (EK-CER), joined by members of an international research group, led the project to analyze the lonsdaleite mineral material from the Canyon Diablo iron meteorite found in the Arizona desert in 1891 using state-of-the-art electron microscopy, crystallography and spectroscopy tests. The researchers found that the shock waves caused by asteroids impacting the Earth create unique diamond-like materials, which, if produced in a controlled fashion, can be used to design materials that are both ultra-hard and ductile. The study summarizing the results was published in the prestigious international journal Proceedings of the National Academy of Sciences on 22 July 2022.
Asteroid impacts produce a high-energy shock wave travelling at a rapid speed, which can in turn generate high temperatures and extreme pressure for a short period of time. This unique geological process favors the development of non-equilibrium conditions and the formation of materials with unusual properties.
Péter Németh, senior research associate at the CSFK’s Institute for Geological and Geochemical Research, and Zsolt Fogarassy, Levente Illés and Béla Pécz, researchers from the EK-CER’s Institute of Technical Physics and Materials Science, together with their international colleagues, studied the lonsdaleite mineral material from the Canyon Diablo iron meteorite found in the Arizona desert in 1891 using state-of-the-art methods for electron microscope, crystallographic and spectroscopic analysis. Named after pioneering British crystallographer Professor Kathleen Lonsdale, the mineral was previously thought to consist of diamond with a purely hexagonal structure, which is different from the familiar cubical, square-shaped crystal lattice diamond.
The results of the current research call into question this thus-far simplified understanding of the structure of lonsdaleite. The researchers established that this lonsdaleite with unique properties, created during an asteroid collision approximately 50,000 years ago, is actually a so-called diaphyte composed of various intergrowths of diamond-graphite nanostructures, which is actually the shared structure of the two materials in a single crystal lattice. Also observable in the mineral are numerous stacking faults occurring in the repeating patterns of the atomic layers.
A diaphyte (diamond–graphite) structure formed during an asteroid impact. The central part outlined with the red diamond symbol (about 1.5 nanometers) represents nanocrystalline diamond, and the green color represents graphite. The transitional color between red and green refers to the transition bond type between diamond and graphite.
Based on the results, the identification of different types of intergrowths between graphene and diamond structures may contribute to a better understanding of the pressure and temperature conditions occurring during asteroid impacts. The researchers found that due to the unique environment of the carbon atoms at the interface between diamond and graphene, the distance between the graphene layers deviates significantly from ordinary measurements. They also observed that the diaphyte structure is responsible for the appearance of a previously unexplained Raman spectroscopic band. This allows the diaphyte structures in the diamond to now be identified using a simple spectroscopic technique, without the need for expensive and labor-intensive electron microscopy.
The complex structures identified in the Canyon Diablo sample can also occur in many other carbonaceous materials. The researchers believe that it is not only the dynamic shock waves created during asteroid impacts that can create diaphyte structures, but also static compression at high pressures and temperatures, as well as chemical vapor deposition. By controlling the layer growth of diaphytes, it could well be possible to design materials that are not only ultra-hard, but also malleable, with tunable electronic properties from the conductor to the insulator. The discovery paves the way for the design of new types of diamond-like materials with exciting mechanical and electronic properties, so new applications can be created in many industrial fields, from abrasives to electronics and nanomedicine to laser technology.
The researchers pay tribute to their late co-author Professor Paul McMillan, who played an important role in the creation of the research group and contributed with tireless enthusiasm to success in the field of diamond research.
The project was realized with the support of, among other sources, the National Research, Development and Innovation Fund and the János Bolyai Research Scholarship of the Hungarian Academy of Sciences.
Publication:
Péter Németh, Hector J. Lancaster, Cristoph G. Salzmann, Kit McColl, Zsolt Fogarassy, Laurence A. J. Garvie, Levente Illés, Béla Pécz, Mara Murri, Furio Corà, Rachael L. Smith, Mohamed Mezouar, Cristopher A. Howard, Paul F. McMillan (2022). Shock-formed carbon materials with intergrown sp3– and sp2-bonded nanostructured units. Proceedings of the National Academy of Sciences, Vol. 119. doi: 10.1073/pnas.2203672119