Carbon is arguably the most important element on Earth. It is the fundamental building block of life and the backbone of all the proteins and fats in our bodies. Still, carbon is more interesting that just in biology. It makes up some of the most popular structures for studies in materials science, like graphene or carbon nanotubes. On a larger scale, carbon atoms, like other elements, tend to organize into repeating structures, which are called crystals. The ways in which the atoms are arranged directly relate to the properties of the final crystal. Diamond, for example, is made entirely of carbon and is the hardest natural material on the planet. Graphite, however, is also made of the same carbon atoms arranged in a different way and is very brittle (think about how easy it is to break the tip of a pencil). Therefore, precise control over the crystal structure of a material allows for scientists to modify a range of interesting properties, like hardness, “stretchability” (or ductility), the appearance of the material, or how well it conducts electricity or heat.
Despite carbon’s presence throughout biology materials science, there remain a fairly limited number of different carbon-based crystal structures. Computational simulations based on quantum mechanics predict that other carbon crystals should be possible theoretically, at elevated temperatures and pressures – but figuring out how to actually make these materials and use them in a normal environment is quite a challenge. Now, researchers from the Carnegie Institution for Science have successfully designed a method to synthesize a new carbon-based structure which should exhibit the hardness and strength of diamond while allowing for scientists to change other properties based on the types of other elements included.
The new structure is a member of the “clathrate” family of crystal structures, in which the main “host” atom (here, carbon) forms a cage-like structure around other “guest” atoms. These cage-like structures have been discovered or synthesized for other host materials, like water or silicon, but never for carbon. Computer simulations suggest that these materials should exist, but scientists have been unsuccessful at making them. Instead of searching for a process using only carbon as the host, the researchers decided to replace some of the carbon atoms making up the cage with a similar element – boron. With this change, they successfully synthesized this brand-new carbon-based structure. The resulting material should exhibit similar hardness and strength to diamond, but by including another element in the “guest” spots within the cages (here, strontium), the material is also electrically conductive, unlike diamond.
Using a carbon-boron framework for this synthesis should allow for new carbon structures to now be developed, with different physical properties that can be tuned depending on the desired application. Still, the structure was stable at a normal temperature and pressure only when kept in an isolated non-reactive environment. Moisture from the air degraded the samples in a matter of hours. The samples made were also relatively small and further testing is required to confirm many of the desirable properties these structures should exhibit. Even so, this is an exciting new step in making the most important element on Earth even more useful.
Managing Correspondent: Andrew T. Sullivan
Press Articles: “‘Superdiamond’ carbon-boron cages can trap and tap into different properties,” Phys.org
Original Journal Article: “Carbon-boron clathrates as a new class of sp3-bonded framework materials,” Science Advances
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