Synthetic diamond with hexagonal lattice outshines the natural kind with unprecedented hardness

A team of physicists, materials scientists and engineers affiliated with several institutions in China, working with a colleague from Umeå University, in Sweden, has grown a diamond that is harder than those found in nature. In their project, reported in the journal Nature Materials, the group developed a process that involves heating and compressing graphite to create synthetic diamonds.

Diamonds are a prized gem the world over. Their sparkling appearance has made them one of the most treasured gemstones throughout human history. In more recent times, because they are so hard, diamonds have also been used in commercial applications, such as drilling holes through other hard materials. Such attributes have kept the price of diamonds high. Because of that, scientists have developed ways to synthesize them, and today, a host of synthetic diamonds are available for sale.

Researchers have previously pursued harder diamonds with hexagonal rather than cubic lattices, which is how most natural and synthetic diamonds form. However, past attempts to make hexagon-lattice synthetic diamonds have resulted in diamonds that were too small and of low purity.

In this new effort, the research team tried a different approach. They developed a process that involved heating graphene samples to high temperatures while inside a high-pressure chamber. By adjusting the parameters of their setup, the researchers found they could get the graphene to grow into a synthetic diamond with hexagonal lattices.

The first diamond made by the group was millimeter-sized and was tested at 155 GPa, with thermal stability up to 1,100°C. Natural diamonds typically range from 70 to 100 GPa and can only withstand temperatures up to 700°C.

The researchers note that it is unlikely diamonds made using their technique would be used for jewelry; instead, they would be used for drilling and machining applications. They also note that they might be used in other ways, such as for data storage or in thermal management applications.

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