Crystal imperfection

Imperfection:- Imperfection affects the property of a crystal such as, mechanical strength, chemical reaction, electrical properties.

Types of imperfection:-
  • Point imperfection
  • Line imperfection
  • Surface imperfection
  • Volume imperfection

  • Point imperfection:- Point imperfection are the imperfect points such as region in a crystal. The size of point imperfection is one or two atomic diameters. Point imperfection are generated due to thermal shock, thermal fluctuations, mechanical deformation, and high energy particles  bombardment. Point imperfection are thermodynamically stable. Point imperfection are different types:-
  1. Vacancy
  2. Schottky's defect
  3. Frenkel's defect
  4. Substitutional impurity
  5. Interstitial impurity
  • Line imperfection:- Line imperfection is also known as dislocation. Line imperfection are one dimensional imperfections in the geometry of a crystal. there are two main sources of dislocations in the crystal of a solid. This imperfections occur due to mishandling during grain growth and mechanical deformation. dislocation decreases the mechanical strength and reduces the electrical conduction of electrical materials.The imperfection can be minimized by use of thermal energy, control on crystallization, prevention of mechanical deformation and use of whisker form of materials. Dislocation are two types:-
  1. Edge dislocations
  2. Screw dislocations
  • Surface imperfection:- Surface imperfection are two dimensional imperfections. It is determined on the surfaces of the crystals. as the atomic bonds do not extend beyond the surfaces of a crystal, the external surface of the crystal is itself an imperfection. Surface imperfection are five types:-
  1. Grain boundary defect
  2. Twin boundary defect
  3. Low angle tilt boundary defect
  4. High angle, inter phase, twist boundary defect
  5. Stacking fault
  • Volume imperfection:- Volume imperfection are three dimensional imperfections. Volume imperfection are generally found inside the solids. These are obtained due to foreign particle inclusions, pore. Due to random location of pores, inclusion present inside the volume of a material.
  • Vacancy:- It is the type of imperfection in which one or more atoms are not found at their respective place. So, a kind of vacant place is created and this type of imperfection is called vacancy imperfection.

  • Substitutional impurity:- In this type of imperfection, when a foreign atom replaced the atom of parent from its lattice point the impurity is called substitutional impurity. The parent atom is called as solvent and the foreign atom is known as solute.

  • Interstitial impurity:- An atom acquired a space between the atom (called voids), hence this interstitial space is filled by one or more atom is called interstitial impurity. These type of imperfection are cause lower the overall strain energy of a structure.

  • Frenkel's defects:- When an ion is displaced from its regular position the defects is called frenkel's defects. When a pair of ion is removed from a compound then the schottky's defect takes place.This defects does not affect the electrical neutrality of the crystal.

  • Schottky's defects:- When a pair of cation and anion is removed from an ionic crystal unit cell it forms a defect known as schottky's defect. This type of defect also maintains the electrical neutrality of the crystal.

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