New Carbon Form Can Indent Diamond
August 17, 2012

New Form of Carbon Observed By Carnegie Scientists

April Flowers for - Your Universe Online

A new form of very hard carbon clusters capable of indenting diamond has been observed by a team of Carnegie Institution for Science researchers.

The carbon clusters are unusual in their mix of crystalline and disordered structures and have potential applications for a range of mechanical, electronic, and electrochemical uses. The team, led by Lin Wang, published their findings in the August 17, 2012, issue of Science.

Carbon comes in many forms — from honeycomb-like graphene, pencil lead graphite, diamond, cylindrically structured nanotubes, to the hollow spheres called fullerenes — and is the fourth most abundant element in the universe.

Some carbon is crystalline — the structure organized in repeating atomic units, and some is amorphous — the structure lacks the long-range order of crystals.  Hybrid forms — which combine both crystalline and amorphous elements — had not previously been observed although scientists believed they could be created.

The Carnegie team of researchers started with  a substance called carbon-60 cages, made of highly organized balls of carbon constructed of pentagon and hexagon rings bonded together to form a round, hollow shape. An organic xylene solvent was put into the spaces between the balls and formed a new structure. Pressure was applied to this combination of carbon cages and xylene solvent to see how it changed under different stresses.

The carbon-60's structure remained at relatively low pressure, but as the pressure increased, the cage structures started to collapse into more amorphous carbon clusters. The clusters retained their original sites forming a lattice structure.

Within a narrow window of pressure, about 320,000 times the normal atmosphere, the new structured carbon is created and does not bounce back to the cage structure when the pressure is removed. Identifying this window is crucial for finding practical applications for the new material going forward.

This new material is capable of indenting the diamond anvil used to create the high pressure conditions, making it a super-hard new material.

The solvent seems to be a crucial element in the new carbon structure. If it is removed by heat treatment, the material loses its lattice periodicity. There are many similar solvents the team intends to test to create an array of similar, but slightly different, carbon lattices.

"We created a new type of carbon material, one that is comparable to diamond in its inability to be compressed," Wang said. "Once created under extreme pressures, this material can exist at normal conditions, meaning it could be used for a wide array of practical applications."