Superdiamond carbon-boron cage
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 or carbon cage technology.
“On a larger scale, carbon atoms, like other elements, tend to organize into repeating structures, which are called crystals. How the atoms are arranged directly relate to the properties of the final crystal”.
Creating carbon cages:
A long-sought-after class of “super diamond” carbon-based materials with tunable mechanical and electronic properties was predicted and synthesized by Carnegie’s Li Zhu and Timothy Strobel.
Carbon is the fourth-most-abundant element in the universe and is fundamental to life as we all know it. It is unrivalled in its ability to form stable structures, both alone and with other elements.
“A material’s properties are determined by how its atoms are bonded and the structural arrangements that these bonds create”.
For carbon-based materials, the type of bonding makes the difference between the hardness of diamond, which has three-dimensional “sp3” bonds, and the softness of graphite, which has two-dimensional “sp2” bonds.
The carbon caging technology:
Despite the enormous diversity of carbon compounds, only a handful of three-dimensionally, sp3-bonded carbon-based materials are known, including diamond.
The three-dimensional bonding structure makes these materials very attractive for many practical applications due to a range of properties including strength, hardness, and thermal conductivity.
Aside from diamond and some of its analogues that incorporate additional elements, almost no other extended sp3 carbon materials have been created, despite numerous predictions of potentially synthesizable structures with this kind of bonding.
Following a chemical principle that indicates adding boron into the structure will enhance its stability, the researchers examined another 3D-bonded class of carbon materials called clathrates, which have a lattice structure of cages that trap other types of atoms or molecules.
“Clathrates comprised of other elements and molecules are common and have been synthesized or found in nature”.
However, carbon-based clathrates have not been synthesized until now, despite long-standing predictions of their existence.
Researchers attempted to create them for more than 50 years. Strobel, Zhu, and their team approached the problem through a combined computational and experimental approach.
They used advanced structure searching tools to predict the first thermodynamically stable carbon-based clathrate and then synthesized the clathrate structure, which is comprised of carbon-boron cages that trap strontium atoms, under high-pressure and high-temperature conditions.
The outcome of the Superdiamond carbon-boron technology:
The result is a 3D, carbon-based framework with diamond-like bonding that is recoverable to ambient conditions. But unlike diamond, the strontium atoms trapped in the cages make the material metallic meaning it conducts electricity with potential for superconductivity at notably high temperature.
“What’s more, the properties of the clathrate can change depending on the types of guest atoms within the cages”.
The trapped guest atoms interact strongly with the host cages. Depending on the specific guest atoms present, the clathrate can be tuned from a semiconductor to a superconductor, all while maintaining robust, diamond-like bonds.
Given a large number of possible substitutions, we envision an entirely new class of carbon-based materials with highly tunable properties. Depending on which element it captures, it has different abilities.”
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