Isotropic crystals & anisotropic crystals

  • Thread starter Wasseem92
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  • #1
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Main Question or Discussion Point

Alright my question is: why do single crystals properties vary with direction (anisotropic) when it is a perfect crystalline structure. I mean doesn't that mean that the atoms are ordered correctly so shouldn't that mean that at every direction its the same magnitude? I really need help because it is confusing me.
 

Answers and Replies

  • #2
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It depends on the lattice direction along which you are measuring the property. For example, Graphite(although polycrystal) is stronger in axial direction than any other.The properties vary because of change in atomic arrangement (atomic spacing, interplanar spacing )in different directions in single crystals. a polycrystal (most of the engg alloys) are isotropic because the multiple orientation of multiple grains results decrease of anisotropy.
 
  • #3
uby
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Let's picture the simplest lattice: primitive cubic. If you are an atom at a corner and look along the edges of the lattice unit cell, your nearest neighbor is one lattice parameter distance away. However, the nearest neighbor when looking in a direction towards the opposite corner of the unit cell will be sqrt(3) times longer, and when looking towards the atom on the adjacent face in the opposite corner will be sqrt(2) times longer. In other words, the linear density of atoms along any given direction varies simply due to the crystal symmetry. Many properties will vary with this linear density, even when all atoms are the same.
 

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