Scientists have developed even harder hexagonal diamonds.

Diamonds are valued worldwide and across various industries for different reasons. Jewelers require brilliance and clarity, while engineers and dentists need hardness. Diamonds are extremely hard, rated 10 out of 10 on the Mohs scale of mineral hardness. Other minerals can be scratched and cut by diamonds. Diamond earrings can scratch the sapphire glass of phones, and diamond cutters effectively work with glass.

The high hardness and extensive industrial applications have led to a demand for synthetic diamonds. Drills and bits with diamond grit successfully process ceramics, teeth, metals, and rocks. Scientists have developed several methods for growing synthetic diamonds for engineering, scientific, and jewelry purposes.

Most natural and synthetic diamonds have a cubic crystal lattice. Researchers have attempted to industrially create harder diamonds with a hexagonal lattice but have produced samples that are too small and of poor quality. Natural diamonds with a hexagonal lattice exist; they are found in meteorite craters and are called lonsdaleite.

An international group of scientists managed to create conditions for the formation of hexagonal diamonds from graphite, an allotrope of carbon with a hexagonal crystal lattice. They heated the material to about 1500 degrees Celsius inside a high-pressure chamber. The researchers discovered that under these conditions, they could induce graphite to transform into synthetic diamond with the desired crystal lattice. The work has been published in Nature Materials.

The diamond created by the scientists, measuring several millimeters, demonstrated a hardness of 155 gigapascals and maintained thermal stability up to 1100 degrees Celsius. Natural diamonds typically have a hardness of 70-100 gigapascals and can withstand temperatures up to 700 degrees Celsius. With further heating, they either transform into graphite in an oxygen-free environment or react with oxygen to become carbon dioxide — CO₂.

Researchers say that the diamonds produced using their technology are unlikely to be used by jewelers. The increased hardness will be appreciated in drilling and material processing, as well as in microelectronics. Synthetic diamonds can serve as substrates for growing transistors and are utilized by scientists in superconductivity research.