What Is Crystal Imperfections?

What Is Crystal Imperfections?

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 is the imperfect points such as regions in a crystal. The size of point imperfection is one or two atomic diameters. Point imperfection is generated due to thermal shock, thermal fluctuations, mechanical deformation, and high-energy particle bombardment. Point imperfection is thermodynamically stable. Point imperfections 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 imperfections are one-dimensional imperfections in the geometry of a crystal. there are two main sources of dislocations in the crystal of a solid. These 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 the 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 imperfections 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 imperfections are five types:-
  1. Grain boundary defect
  2. Twin boundary defect
  3. Low angle tilt boundary defect
  4. High angle, interphase, twist boundary defect
  5. Stacking fault
  • Volume imperfection:- Volume imperfections are three-dimensional imperfections. Volume imperfection is generally found inside the solids. These are obtained due to foreign particle inclusions, pores. Due to the random location of pores, inclusion is 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 a parent from its lattice point the impurity is called substitutional impurity. The parent atom is called a 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 atoms is called interstitial impurity. These types 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 are called Frenkel's defects. When a pair of ions is removed from a compound then the Schottky defect takes place. This defect 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 defect. This type of defect also maintains the electrical neutrality of the crystal.

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