Performance and life of any solid engineering structure depends greatly on its material. Materials Science (MS) is a subject that deals with the solid material, its internal structures, properties, variation of such properties and of course developing new materials.

Most of the engineering materials are solid and thus MS focuses mainly on solid materials. Solid materials can be broadly classified into three groups—metal, ceramic and polymer. Composites can be obtained by combining any two or all three of the above basic classes of solid. Solid materials can again be crystalline or amorphous. When every atoms in a solid is arranged in a specific manner and there is no defect or imperfection, then that solid is called crystalline. Otherwise, the solid can be considered as amorphous.

Every physical material in this world is composed of huge number of atoms. The radius of an atom of any material is very small; in fact, it is not visible by bare eyes. For example, atomic radius of iron atom is just 126 Pico-meter (1.26×10-10 meter). If you consider it in mass basis, then also 1gm of iron contains around 1.1×1022 atoms.

Now, do you believe that all these atoms will always be present in the material and there will be nothing missing? Think practically. Always there will be some missing atoms and this will lead to defect. Defect or imperfection can also occur if atoms of other materials remain present within it. So let us define the term ‘Imperfections in solids’. Since most of the engineering applications are based on solid materials (compared to liquid and gaseous materials), so our discussion on defects will remain confine within solids.

Imperfections in solid (crystal defects)

A solid can be termed as defective if one or more atoms remain absent permanently from their corresponding lattice site or foreign atoms occupy either the lattice site or in interstitial position. Defects in solids can be broadly classified into four categories—Point Defect, Line Defect, Surface Defect and Volume Defect. Various types of defects, their characteristics, impact on various properties, determination of number of defects, etc. are discussed here. Browse all topics.