Types Of Point Defects

Imperfection in solids refers to any abnormality in the pattern of crystal arrangement in solids. When crystals are formed, faults occur. It might arise at a very rapid or a moderate rate. This occurs as a result of particles lacking sufficient time to arrange themselves in a regular way.

Point defects describe the flaws in solids and the various sorts of point defects. Crystalline solids are created by the assembly of many tiny crystals. Following the crystallization process, many sorts of faults are discovered in crystals. Point defects are imperfections that occur exclusively at or around a single lattice point. They are not enlarged spatially in any dimension. Generally, no explicit limitations on the size of a point defect are specified. On the other hand, these errors frequently involve only a few additional or missing atoms. Typically, dislocation loops are conceived of as greater defects within an orderly structure. Numerous point defects, particularly in ionic crystals, are historically referred to as centers: for example, a vacancy in a large number of ionic solids is referred to as a luminescence center, a color center, or an F-center. These dislocations enable ion transport through crystals, resulting in electrochemical reactions.

When the crystallization process occurs rapidly, point defects are catered for. These flaws are primarily caused by the misalignment of the constituent particles. When the ideal arrangement of solids is deformed around a point/atom in a crystalline solid, this is referred to as a point defect.

The Frenkel type, the Schottky type, and the impurity type are all examples of point defects. The Frenkel defect occurs when a single ion is displaced from its typical lattice location and moves to a nearby interstice, or space between lattice atoms. Two ions of opposing sign escape the lattice in the Schottky defect. Impurity defects are foreign atoms that either replace part of the solid’s atoms or squeeze into the interstices; they play a significant role in the electrical behavior of semiconductors, which are materials used in computer chips and other electronic devices.

In crystalline solids, defects or imperfections are classified into four types: line defects, point defects, volume defects, and surface defects. Historically, crystal point defects were initially seen in ionic crystals, rather than in much simpler metal crystals.

Point defects are classified into three types:

• Stoichiometric defect
• Frenkel defect
• Schottky defect

1. Stoichiometric Defect: This type of point defect does not affect the ratio of positive to negative ions (Stoichiometry) or the electrical neutrality of a solid. It is occasionally referred to as intrinsic or thermodynamic flaws.

They are fundamentally divided into two categories:

• When an atom is not present at one of their lattice sites, that lattice site becomes vacant, resulting in a vacancy defect. As a result, a substance’s density reduces.
• A defect in which an atom or molecule occupies the intermolecular gaps in crystals is called an interstitial defect. The density of the substance increases as a result of this defect.

A non-ionic compound is characterized mostly by vacancy and interstitial defects. The Frenkel and Schottky defects are identical in an ionic molecule.

2. Frenkel Defect: In general, in ionic materials, the smaller ion (cation) displaces the larger ion (anions) and takes up intermolecular space. In this situation, it creates a vacancy defect in its original position and experiences an interstitial defect in its new position. Additionally, it is referred to as a dislocation defect. A substance’s density remains constant. This occurs when the anions and cations have a significant size difference. ZnS and AgCl are two examples.
3. Schottky Defect: Ionic Solids contain this type of vacancy defect. However, in ionic compounds, we must balance the electrical neutrality of the complex such that an equal number of anions and cations are absent. It decreases the substance’s density. Cations and anions are nearly identical in size in this.

CONCLUSION- 

When the crystallization process occurs rapidly, point defects are catered for. These defects are primarily caused by misalignment of the constituent particles. When the ideal arrangement of solids is deformed around a point/atom in a crystalline solid, this is referred to as a point defect.

Impurity defects are foreign atoms that either replace part of the solid’s atoms or squeeze into the interstices; they play a significant role in the electrical behavior of semiconductors, which are materials used in computer chips and other electronic devices.