A powder is a collection of a large number of powders and grains such as sand, salt, wheat, or coastal pebbles, which behave like a solid at first glance but sometimes exhibit a liquid-like fluidity.Examples are landslides caused by earthquakes and avalanches in sandy mountains.Moreover, the size of the powder and grains is so macroscopic that the movement is not affected by "thermal fluctuation", and energy is dissipated in the event of a collision.

　Therefore, it shows a complicated crystallization mechanism, such as the need for intermittent energy supply for powder crystallization.Although powders have been discussed by statistical methods in the past, they cannot be applied to other than low-density powders, and the structure and properties of high-density powders and mathematical description methods have not been known.

　Therefore, the research group acquired experimental data of powder consisting of a collection of spheres by 3D X-ray tomography.A mathematical method called a persistent diagram, which characterizes the information of holes in the data, was applied to quantitatively classify the cavities contained in the powder system.As a result, it was discovered that as the density increases, the crystal structure changes to a regular tetrahedron or a regular octahedron via four deformation mechanisms.In addition, an analytical mathematical formula for the deformation process is also specifically derived.We clarified how the powder crystallizes by changing its arrangement according to the change in density.

　This result will advance the understanding of phenomena in which voids are important, such as the mechanical structural stability of powders, aggregation due to vibration, and geological fluidity, and is expected to be applied to fields such as soil problems and geology. There is.

Paper information: [Nature Communications] Pore configuration landscape of granular crystallisation