Imperfections in Solids

Even though crystalline solids possess long range order, real crystals are not perfect. A solid is usually an aggregate of many small crystals, and these carry defects — especially when crystallisation happens at a fast or moderate rate. Only when crystallisation is extremely slow do we get single crystals, and even those are not entirely defect-free.

Defects are basically irregularities in the arrangement of the constituent particles. Broadly they are of two kinds:

• Point defects — irregularities around a single point or atom in the crystal.
• Line defects — irregularities along entire rows of lattice points. …