Types of Defects in Solid

In solids, the crystal arrangement is in a symmetrical pattern and it’s called imperfection or defect in solids. For the formation of crystal processes, defects take place. Defects happen in a very fast way because particles are closely packed in a solid they do not rearrange themselves. Small crystals arranged together closely make a solid. 

Crystal defect:-

Absolute crystals are formed only at 0K temperature, and other crystals are not absolute. Crystal defect can be defined as the withdrawal of complex order and particles’ periodic arrangement in the crystal lattice. 

Cause of crystal defect:- 

Crystal defect takes place in following factors- 

• Lattice vacancies
• In a lattice, disturbance of particles.
• A non-stoichiometric amount of ions.
• Lattice impurities.

Types of defects in solids:- 

 Mainly classified into two types- 

• Point defect.
• Line defect.

Line defect:- 

In line defect, solid expands above the microscopic region in a row of the crystal lattice.

Point defect:- 

In lattice, disturbance of particles, as they move from one place to another cause the imperfection or defect in the crystal lattice. There are three types of point defects.

Types of point defects:- 

There are mainly three types of point defects – 

• Stoichiometric defect
• Non- stoichiometric defect
• Impurity defect

Stoichiometric defect:- 

This defect is defined as the ratio of cation and anion enduring similarly or we can say that substance stoichiometry is not interrupted and hence called stoichiometry defect. These defects are also known as intrinsic or thermodynamic defects. These defects can be detected in non-ionic and ionic solids both. There are two types of stoichiometry defects.

Vacancy defect :- 

When there is the absence of particles in some place in a lattice and create a vacancy called vacancy defect. Mainly these defects can be seen in non-ionic solids and metals, crystal density is decreased due to this defect. 

Interstitial defect:- 

In a lattice, if there is an addiction of constituent particles on the interstitial site called interstitial defect. This defect can be seen in non-ionic solids and metals. But instead of decreasing the vacancy defect, this defect increased the crystal density. 

Schottky defect:- 

This kind of point defect was developed by German scientist Schottky in the year 1930. In this defect, cations and anions are missing from a lattice, in an equal amount. This defect brings down the density of particles but does not affect the crystal stoichiometry. In a lattice, atoms can move freely with the help of a facile mechanism due to Schottky’s defect.

Example- NaCl, KCl

Outcomes of Schottky defect:- 

• The density of solid is decreased.
• For the movement of ions or atoms, this defect provides a facile mechanism.
• Stoichiometry of this defect is not affected.

Frenkel defect:- 

This defect can also be known as dislocation defect and was observed by scientists in the year 1926. Frenkel defect is defined as the ion release from its regular site and bind on the interstitial site. Mostly occupied on that crystal in whose cation and anion are irregular in size. This defect also provides a facile mechanism for the movement of ions and also does not have any impact on density.

Example- AgCl and AgBr

Outcomes of Frenkel defect:-

• This defect does not have an impact on density.
• For the movement of ions and atoms, this defect provides a facile mechanism.

Non- stoichiometric defect:- 

This defect can be happened due to two reasons- 

• In a lattice, substances have a cation whose proportion is more than in an anion. And hence known as a metal excess defect.
• In a lattice, substances have a cation whose proportion is lesser than in an anion. And hence called a metal deficiency defect.

This defect is classified into two main types-

Metal excess defect- 

It happens when in a lattice, cation has more ratio than in anion. There are further two types- 

Anionic vacancy:

In this defect, to maintain electrical neutrality, electrons bind to that space where an anion is released. An anion trapped electron to catch them is referred to as f- centre. The cavities present are coloured centres.

Example – NaCl and LiCl

Extra cation:

In the lattice, extra cation binds to interstitial sites. And hence extra positive charge is created which is further maintained by electron numbers.

Example- zinc oxide

Metal deficiency defect-

It happens when in a lattice, cation has less ratio than in anion. Different oxidation states are varied by compound cations.

Example- iron compound crystal and copper compound crystal.

Impurity defect:- 

The addition of ions with different oxidation states is carried out by chemical impurities called impurity defects. This defect can make a vacancy of captions in a lattice. Impurities that can be added to crystals are called doping. Impurities are added in ions or the presence of an ionic solid. an n-type semiconductor is formed when doping is with impurities of electrons. A p-type semiconductor is formed when doping with a defective electron.

Conclusion:-

The microscopy technique was used to study defects in solids. In some defects the density of solid increases, in some density is decreased and in some solid, it doesn’t affect. Some defects help to maintain the charge of electrons and some variation in cations and anions. In the above article, we learned about many defects that happen in solids. Mainly defects of solid are of two types – line and point defect and then point defect is further classified in three different types. Types of defects in solid explain various features of defects and reason behind imperfection of solid.