Hexagonal Diamond Is Real. But Which Study Should You Actually Believe?

A research team from Nanjing University published a paper in Nature on March 5, 2026, confirming the synthesis of bulk hexagonal diamond, a rare carbon structure also known as lonsdaleite, in millimeter-sized, phase-pure form. The team, led by Lai, Shoulong and colleagues, compressed highly oriented pyrolytic graphite along its crystal axis using 20 gigapascals of pressure at temperatures between 1,300 and 1,900 degrees Celsius. They confirmed the hexagonal lattice using X-ray diffraction and atomic-resolution electron microscopy. Hardness measured at 114 GPa along the axial direction, compared to natural cubic diamond's roughly 110 GPa on its comparable surface.

That was the paper covered by every major outlet. It wasn't the only relevant paper published in the past year.

The Number the Coverage Missed Was Published First

A separate team published results in Nature Materials in early 2025 with a different synthesis approach and a notably different result: 155 GPa. That study, from Chen et al., used an intermediate "post-graphite phase" pathway, compressing graphite to higher pressures before applying heat. Their sample also demonstrated thermal stability up to 1,100 degrees Celsius, compared to roughly 900 degrees for standard industrial nanodiamonds. These two papers describe two different methods producing the same material at materially different hardness values, and almost no outlet covering the March 2026 Nature publication mentioned the prior Nature Materials result from 12 months earlier.

That gap matters directly for how you evaluate the headline number. The 114 GPa figure from Lai et al. is a solid, consistent measurement on the purest phase-pure sample ever made. It is a modest 4% improvement over cubic diamond. The 155 GPa figure from Chen et al., if it holds up to replication, is a 40% improvement. These aren't minor variations in the same result. They're potentially different material performance ceilings depending on synthesis route. The theoretical maximum, cited since a 2009 Physical Review Letters paper by Pan, Zhisheng and colleagues, sits at roughly 58% harder than cubic diamond, suggesting real performance could land almost anywhere across a wide band.

The existence debate is settled. The performance question isn't.

What this means practically: the synthesis route determines the output. Lai et al.'s method produces a purer phase with confirmed hexagonal structure. Chen et al.'s method may produce a harder material via a different transformation pathway. Whether those can be combined, or whether one approach scales while the other doesn't, is precisely where the field will spend the next several years. Oliver Tschauner, a crystallographer at the University of Nevada, Las Vegas, noted when the Lai et al. results were published that hundreds of researchers had previously claimed to observe hexagonal diamond, and most hadn't. The rigor of the confirmation matters as much as the hardness number.

The Industrial Race Worth Tracking Right Now

The commercial implications are not imminent, but the competitive signals are visible. China has been building its synthetic diamond manufacturing capacity deliberately for over a decade. Both the Lai et al. team and the Chen et al. team operated out of Chinese research institutions. Element Six, a De Beers subsidiary based in the UK, currently dominates commercial synthetic cubic diamond production for industrial cutting tools and semiconductor substrates. DeBeers has not publicly commented on the hexagonal diamond results.

The specific application worth watching is power electronics. Cubic diamond is already being developed as a semiconductor substrate for high-voltage, high-frequency devices that run hotter and faster than silicon. Companies including Element Six and several Japanese research institutes are active in this space. If hexagonal diamond can be produced with the quality needed for semiconductor-grade substrates, the 1,229 GPa Young's modulus measured by Lai et al. (compared to 1,087 GPa for cubic diamond) matters for wafer performance under mechanical stress. Follow patent filings from Chinese materials labs and from Element Six's research arm over the next 18 months. That's where the commercial intentions will show first.

The science of hexagonal diamond's existence is now settled. The race to make it useful is just beginning, and the countries and companies paying attention to synthesis routes today will have a head start when scale becomes achievable.