Crystal Defects

Hi, what are you guys up to?

Anyway, next week I’ll have mid-test for this term (*yeay) and here I’ll try a kind of different way of study. I’ll review the material of my Physical Metallurgy class about Crystal Defects.

Ok. Let’s start. First of first, you have to remember that NOTHING IS PERFECT in this real-world, including crystal. One of the most famous British physicist, Colin Humphreys said “Crystals are like people. It is the defects in them which tend to make them interesting”. Real crystals are never perfect, there are always defect. And you know what? The task of Materials engineers is not to completely remove the defects (coz that’s impossible to do), but to engineer the defects to increase the quality of materials property.

 

The image above shows the structure of single crystal which (almost) has no defect and poly-crystal with many defects.

The presences of a relatively small numbers of defects have a profound impact on macroscopic properties of materials and materials engineers should control the defect in order to get the properties required without adding another material or without change the composition. So, we can draw a conclusion that the properties of a material also depends on defects (beside bonding and structure).

The crystal defect classified by their dimension. The 0-dimensional defects are called Point Defects, 1-dimensional are called Line Defect, 2-dimensional defects are surfaces or interfaces, and 3-dimensional defects change the crystal pattern over finite volume. Here’s the explanation of those defect.

0-Dimensional Defect

a.    Vacancy; when an atom is missing from a position that ought to be filled in the crystal.

b.    Interstitialcy; when an atom occupies an interstitial site where no atom would ordinarily appear.

((to be continued....))