A perfect crystal very rarely occurs in nature and is very difficult to produce artificially. All crystals contains faults. Sometimes, they contain too many faults (or too few) and the result is reduced properties being less tough, having less strength and being less stiff.
To remind ourself of the above terms:
- Toughness – energy needed to cause failure. It is in per unit area or per unit volume. The energy is transferred via work. W = F x D. Tough materials can be ductile and/or malleable.
- Stiff materials have a high Young Modulus (Pa).
- Strength – failure force or failure stress.
There are also other variations in materials with crystalline structures:
- Dislocation – it is when the crystalline structure is disturbed causing there to be a permanent partial shift.
- Occlusions – this is when there is an interstitial space (a missing atom).
- Grain Boundary – Here we have two large grains, the edges of which are marked by blue lines. There is also at least one missing atom, marked with a red dot. The area between the grains is typically messy and little structured.
- Dopant atom – this is an atom of a different element in the crystal structure.