# What kind of crystal have anisotropy

We now know that many properties of the materials come from the (crystal) bond. The exact shape of the potential well of a bond gives us:That's quite a lot. But if we know the crystal structure, i.e. lattice and base, we know a little more.All of the above properties (and many more) can appear in two variants:
• isotropic; d. H. the same property is measured in any direction, e.g. B. the same value of E.Module.
• anisotropic; d. H. the property is a function of the crystal direction and many more
Brief (or longer) reflection leads to the conclusion that all grids must automatically lead to anisotropic properties!If you don't believe it, calculate it E.Module as a function of and many more. Note: Since the E.Module is the "spring constant" of the binding in relation to a unit area, the number of bindings per unit area must be counted.We know from (hexagonal) graphite that the {001}-Crystal planes are very easy to move against each other, but perpendicular to it "nothing works". It doesn't get any more anisotropic. This property is used in a targeted manner in the "pencil" or in graphite lubricants; also in CFRP (Carbon-fiber-plastic composite).The question that arises is: Why do you "actually" not notice the anisotropic behavior of most crystals (e.g. stones or hex. Metals)? The answer is:1. Most of the crystals are polycrystals. In each grain the properties are anisotropic. Averaged over many grains with statistically distributed directions, however, we find an isotropic mean.2. The anisotropy is definitely there, but the layman does not notice it because he does not see through the connections. For example, the hexagonal close-packed metals are like Mg significantly more brittle than the cubic ones fcc- or bcc-Metals, and this is both a direct consequence of the anisotropic hexagonal crystal structure and a major technical problem.

© H. Föll (MaWi for ET&IT - Script)