Bulk hexagonal diamond emerges from graphite under high pressure, resolving a long-standing debate

A Nature study reports the synthesis of millimeter-sized, phase-pure bulk hexagonal diamond (HD) from highly oriented pyrolytic graphite under high-temperature, high-pressure conditions, with structural and computational confirmation. HD shows slightly higher hardness than cubic diamond and strong thermal stability, resolving the long-standing question of HD’s existence and offering new insight into graphite-to-diamond transformation and potential applications in advanced technologies.