Nanjing University Team Publishes Bulk Hexagonal Diamond Synthesis Breakthrough in Nature

The Groundbreaking Synthesis of Bulk Hexagonal Diamond

In a landmark achievement for materials science, researchers from Nanjing University and collaborators, including Zhengzhou University, have successfully synthesized bulk hexagonal diamond (HD), also known as lonsdaleite, and published their findings in Nature on March 4, 2026. This rare carbon allotrope, previously only found in tiny quantities within meteorites, has now been produced in millimeter-sized, nearly pure crystals. The breakthrough resolves decades of debate over HD's existence as a distinct phase and opens doors to revolutionary applications in superhard tools and advanced electronics.

Hexagonal diamond's unique structure promises superior mechanical properties compared to the common cubic diamond (CD), the current benchmark for hardness and thermal conductivity. This development underscores China's rising dominance in high-pressure materials research, positioning universities like Nanjing and Zhengzhou as global leaders.

Hexagonal Diamond vs. Cubic Diamond: Key Structural Differences

Cubic diamond, with its face-centered cubic lattice, is renowned for its extreme hardness (Vickers ~110 GPa), wide bandgap (5.5 eV), and high thermal conductivity (~2000 W/mK), making it ideal for cutting tools, semiconductors, and heat sinks. Hexagonal diamond, however, features a wurtzite-like hexagonal close-packed structure (space group P6₃/mmc), where carbon layers stack in an ABAB pattern rather than ABCABC.

This arrangement results in one shorter, stronger interlayer bond, theoretically boosting hardness by up to 58% and stiffness. Lab tests on the new bulk HD confirmed a Vickers hardness of ~114 GPa, slightly exceeding CD, alongside enhanced thermal stability up to 1100°C. Such properties could transform industries reliant on diamond's limits.

• Hardness: HD ~114-155 GPa (predicted/measured) vs. CD 110 GPa
• Structure: Hexagonal stacking for denser bonding
• Bandgap: Similar wide gap, ideal for semiconductors

The Collaborative Team Behind the Discovery

Led by Prof. Chongxin Shan at Zhengzhou University, a top-ranked institution in China's materials science (#19 globally per US News), the team included Prof. Jian Sun from Nanjing University, a computational physicist specializing in high-pressure phases. Nanjing University, renowned for physics and materials research, contributed theoretical modeling, while experiments used Zhengzhou's Kawai-type large-volume press.

This collaboration exemplifies inter-university synergy in China, where state investments in high-pressure facilities have propelled breakthroughs. Prof. Sun's prior work on carbon phases under extreme conditions was pivotal.

Step-by-Step Synthesis: High-Pressure High-Temperature Innovation

The method employs a two-step high-pressure high-temperature (HPHT) process using highly oriented pyrolytic graphite (HOPG) or single-crystal graphite:

1. Compression: Uniaxial pressure (~20 GPa) along graphite's c-axis in a diamond anvil cell or large-volume press, forming post-graphite phases like M-carbon or nano-graphite.
2. Heating: Laser or resistive heating to 1300–1900°C under sustained pressure, triggering phase transition to HD via layer-by-layer rearrangement.
3. Recovery: Pressure release yields stable, bulk crystals (100 µm to mm-sized) with >99% purity.

This uniaxial stress mimics meteorite shock waves, avoiding cubic stacking faults.

Advanced Characterization Validates Purity and Structure

Rigorous multi-technique analysis confirmed HD:

• Synchrotron X-ray diffraction (XRD): Characteristic peaks matching P6₃/mmc.
• Atomic-resolution STEM/ADF: Hexagonal stacking faults absent, pure ABAB layers.
• Raman/EELS/XPS: Pure sp³ bonds, no graphite sp² signals.

Nanoindentation showed superior indentation resistance.Read the full Nature paper

Overcoming Decades of Challenges in HD Research

Discovered in 1967 in Canyon Diablo meteorite, HD remained elusive due to instability and contamination. Early lab claims (1960s explosions) produced impure nanograins. Recent nano-HD from detonation or CVD failed bulk scale. This 2026 work is the first bulk pure synthesis, settling debates.

Transformative Applications Across Industries

HD's properties enable:

• Superhard Tools: Drilling geothermal wells, aerospace machining (higher heat tolerance).
• Electronics: Ultimate wide-bandgap semiconductor for power devices, outperforming SiC/GaN.
• Optics/Quantum: Enhanced thermal management, quantum sensors.

Global diamond market ($100B+) could expand with scalable HD.Phys.org coverage

Boosting China's Higher Education in Materials Science

This feat highlights China's investment in research infrastructure, with universities like Nanjing (top physics) and Zhengzhou (materials powerhouse) leading. Zhengzhou ranks #19 in China for materials science, fostering research jobs and PhD programs. It attracts global talent, aligning with national goals for sci-tech self-reliance.

Similar advances (e.g., super diamond variants) position Chinese HEIs as hubs for higher ed jobs in cutting-edge fields.

Expert Views and Future Research Horizons

Ho-Kwang Mao (HPSTAR): "Resolves HD controversy, paves way for tech apps." Eiichi Nakamura (Tokyo): "Definitive evidence of bulk HD."

Outlook: Scale-up production, doping for semiconductors, hybrid CD-HD materials. Opportunities abound for higher ed career advice in materials.New Scientist analysis

Photo by Shawn Tang on Unsplash

Career Opportunities and Next Steps in Diamond Research

This breakthrough spurs demand for experts in high-pressure physics. Nanjing and Zhengzhou seek postdocs, faculty via university jobs. Explore Rate My Professor for insights, or higher ed jobs in China. For career growth, check academic CV tips.

China's materials ecosystem offers actionable paths: Join labs, pursue PhDs, innovate in semiconductors.