China Successfully Synthesizes Pure Hexagonal Diamond, Revealing Superior Properties
Researchers in China have reported the successful synthesis of pure samples of hexagonal diamond, also known as lonsdaleite, in a laboratory setting. This achievement provides direct experimental evidence for its existence as a distinct carbon phase and allows for the precise measurement of its properties.
Initial tests indicate it is stiffer, harder, and more oxidation-resistant than conventional cubic diamond.
The study outlines a method for its production and suggests various potential applications.
Background on Hexagonal Diamond
Hexagonal diamond (lonsdaleite) is a theorized variant of carbon characterized by its atoms arranged in a hexagonal lattice, which contrasts with the cubic structure of natural diamond. The concept of hexagonal diamond was first theorized in 1962, with initial laboratory creation reported in 1967.
Previous detections of lonsdaleite primarily occurred in meteorites, such as the Canyon Diablo and Goalpara meteorites, which are believed to originate from shattered dwarf planets or meteorite impact sites.
The existence and specific physical properties of hexagonal diamond have been subjects of scientific debate. Early detections in natural samples were sometimes questioned, with some scientists suggesting the evidence could indicate flawed cubic diamond. The absence of pure samples had previously hindered the precise measurement of its properties.
Laboratory Synthesis Breakthrough
The recent synthesis was conducted by researchers, including those from China's Henan Key Laboratory of Diamond Materials and Devices. The team successfully produced several pure hexagonal diamond samples, each approximately 1.5 millimeters (0.06 inches) in diameter.
The production method involved compressing highly organized graphite for 10 hours. This graphite was placed between tungsten carbide anvils and subjected to 20 gigapascals of pressure, equivalent to approximately 200,000 times Earth's atmospheric pressure. The process was carried out at temperatures ranging from 1,300 to 1,900 degrees Celsius (2,300 to 3,450 degrees Fahrenheit). The study noted that at higher temperatures and pressures within this range, the lonsdaleite began to transform into cubic diamond.
Confirmed Structure and Remarkable Properties
To confirm the material's structure and purity, scientists utilized X-ray diffraction to map atomic positions and advanced microscopy to observe the unique hexagonal stacking patterns of the carbon atoms.
Mechanical property tests, performed by pressing a diamond tip into the sample, showed the synthesized hexagonal diamond exhibited a hardness of approximately 114 gigapascals. This value is slightly higher than that of many natural cubic diamonds, which typically have a hardness of around 110 gigapascals.
The research further indicated that hexagonal diamond is both stiffer and exhibits significantly higher resistance to oxidation compared to cubic diamond.
This superior oxidation resistance allows hexagonal diamond to tolerate elevated temperatures without significant surface degradation.
Implications and Promising Applications
The findings, published in Nature on March 4, are reported to resolve previous uncertainties regarding the existence of hexagonal diamond as a distinct carbon phase and offer new insights into graphite-to-diamond phase transitions. The study also presents a practical strategy for potentially producing hexagonal diamond in bulk.
Potential applications for hexagonal diamond include enhancing existing tools and processes that rely on cubic diamond. These may include:
- Cutting and drilling tools
- Abrasive coatings for polishing
- Heat dissipation in electronics
- Thermal management
- Quantum sensing
Chong-Xin Shan, a co-lead physicist on the study, highlighted these potential applications. Furthermore, the presence of hexagonal diamond in meteorites may provide information regarding the formation and origin of these extraterrestrial objects, offering insights into the solar system.