The research team sintered crystallites with the largest size of tens of nanometers together to form a "nanopolycrystalline" state of diamond, and then applied ultra-high pressure to it to investigate its strength. The experiment was carried out with the laser XII laser with the largest pulse output power in Japan. Observation found that when the maximum pressure of 16 million atmospheres (more than 4 times the pressure of the center of the earth) is applied, the volume of diamond is reduced to less than half of the original.

The experimental data obtained this time show that the strength of nano-polycrystalline diamond (NPD) is more than twice that of ordinary single crystal diamond. It was also found that NPD is the strongest among all materials investigated so far.