Question

Why is crystal structure isotropic although unit cells are anisotropic?

Answer 1

Isotropic and Anisotropic

• The physical and chemical characteristics of isotropic materials are the same in all directions, whereas anisotropic materials have varied properties in various directions.
• Isotropic materials include glass, cubic symmetry crystals, diamonds, and metals.
• Anisotropic materials include wood, composite materials, and all crystals (save cubic crystals).

Crystal structure is isotropic, although unit cells are anisotropic

• When considering a unit cell, the planar density, linear density, and other parameters change on different planes.
• As a result, unit cells are anisotropic, indicating they have distinct characteristics in various planes.
• However, when considering the polycrystal structure, which is generated by the repeating of unit cells in all crystallographic orientations, the grains (crystals) are highly randomly oriented, and the average of the attributes in different directions is the same.
• As a result, the crystal structure is isotropic even though the unit cell is anisotropic.