Hexagonal Diamond (HD)
July31, 2025
Hexagonal Diamond (HD): Breakthrough in Bulk Synthesis and Characterization
Hexagonal diamond (HD), long hypothesized to possess superior physical properties to cubic diamond, has eluded definitive characterization for over half a century due to its occurrence only in disordered mixtures of nanocarbon phases. Recently, however, bulk HD has been successfully synthesized and recovered through controlled compression and heating of high-quality graphite single crystals under quasi-hydrostatic conditions.
This method enabled the formation of highly ordered HD samples ranging from 100 μm to millimeter scale. Structural analysis revealed direct crystallographic transformation pathways—specifically graphite (10-10) to HD (0002) and graphite (0002) to HD (10-10). The resulting material is composed of a threefold intergrowth of densely packed ~100 nm HD crystallites, with minor inclusions of cubic diamond.
Notably, HD features shortened interlayer bonds relative to intralayer bonds, optimizing its crystal structure. While its hardness is only marginally higher than that of cubic diamond, ongoing efforts aim to further improve HD quality by refining graphite precursors and synthesis pressure–temperature (P–T) conditions.
Read more
https://www.nature.com/articles/s41586-025-09343-x
