Frenkel Defects: Definitions, Examples, Characteristics, Calculation, Formula, Formation, Consequences, and Key Differences

Frenkel Defects Overview

When studying the molecular theory of the condensed state, Russian physicist Yakov Frenkel made the discovery of the Frenkel Defect. This finding was significant, though, since it helped to explain a flaw in crystalline solid molecules where an atom or ion would leave its original lattice site unfilled and occupy a different, intermediately vacant position on the same crystal. The flaw, often referred to as a dislocation Defect, also shows both self-interstitial and vacancy faults. 

Who is Frenkel?

Soviet physicist Yakov Il'ich Frenkel, who lived from 10 February 1894 to 23 January 1952, is well known for his contributions to condensed matter physics. He also goes by the name Jacov Frenkel and is commonly referred to as J. Frenkel in English-language media.

What are Frenkel's Defects?

When an atom or cation moves from its initial location in the lattice structure to fill a vacancy while occupying another interstitial position inside the solid crystal, the result is a point Defect known as a Frenkel defect. This flaw results in an interstitial flaw at the new site and a vacancy flaw at the previous site. A dislocation defect is another name for the Frankel Defects. The cation has relocated to a new location between the cations and anions, as seen in the picture, leaving its original lattice position unoccupied.

Examples of Frenkel Defects

Ionic solids with a significant size difference between the cation and anion—the cation typically being smaller due to a higher effective nuclear charge—show Frenkel flaws. The following are some examples of solids with Frenkel flaws-

1. NaCl (Sodium Chloride)
2. Silver (I) Bromide
3. Silver (I) Chloride
4. Silver (I) Iodide
5. Zinc sulfide

Characteristics of Frenkel Defects

The crystal remains neutral and the balance of cations and anions is maintained in the Frenkel Defects, which is a rare Defects. The smaller atoms occupy the interstitial spaces because cations and anions differ in size. The following are the characteristics of Frenkel Defects-

1. As the ions with similar charges get closer, the dielectric constant rises.
2. Due to the existence of unoccupied lattice sites, materials with Frenkel defects exhibit conductivity and diffusion in their solid state.
3. Ionic compounds' chemical composition is impacted by this flaw.
4. Only when cations are smaller than anions does this flaw manifest itself. 
5. Substances also preserve their electrical neutrality under such circumstances.
6. The Frenkel Defects have no discernible effect on the solid's density either, preserving the solid's volume and mass in the process. 
7. The lattice energy and stability of crystalline solids are reduced as a result of the Frenkel Defects. 
8. The solid's entropy grows.

Calculation of the Number of Frenkel Defects

The following are crucial factors to consider while determining how many Frenkel defects there are in a crystal-

1. Positions normally held.
2. The number of positions open.
3. The Defects' release of enthalpy.
4. The temperature in the location.

Read more related articles about the Enthalpy in the table below-

Formula of Frenkel Defects

The formula below may be used to compute Frenkel defects-

Formation of Frenkel Defects

There are several ways that the Frenkel Defects might develop. The following is the list of processes that may be used to explain how the Frenkel Defects develop-

1. As a result, the initial space of the cation, which is reserved for an interstitial space, will become vacant.
2. Depending on its size and the quantity of available space, a cation usually migrates from its initial lattice site to another interstitial site.
3. This cation, which is present in the interstitial space, prefers to settle at locations with lower repulsion, allowing it to occupy the interstitial area.

Reason for the Formation of Frenkel Defects

As the locations of molecules or atoms are established by the unit cell parameters in crystals at repeated set distances, defects are frequently seen in solid-state systems. Particle irradiation is typically used to engineer Frenkel flaws. The majority of a crystal's structure is flawed and unstable. The equilibrium in particle irradiation does not approach the detection limit because the enthalpy at the moment of creation is larger than it is at any other point. When the cation (smaller ion) is displaced in a structure, Frenkel Defects can also happen by accident.

Impact of Frenkel Defects on Density

The density and stability of the crystal are unaffected by the Frenkel Defects. The Defects directly affect the ion's movement, but they have no effect on the solid-state structure's volume or density. The interstitial atoms in densely packed formations cause stresses that cause the lattice to expand. This expansion outweighs the lattice's contraction as a result of the created void.

Consequences of Frenkel Defects

In ions, the Frenkel Defects result in a displacement. Due to the smaller cation ion's displacement from its original location and placement in an interstitial site, this Defect is also known as the dislocation Defect. The compounds have low coordination numbers and a significant variance in the sizes of the anions and cations, despite the fact that the density is unaltered.

Key Difference Between Schottky and Frenkel Defects

In solid-state crystals, defects are caused by the development and seclusion of the crystals. Frenkel imperfection signifies the production of crystalline ionic compounds, whereas Schottky Defects highlight the imperfection in crystalline solids. The key differences between them are given below-

Points to Remember

1. A vacancy is generated when a tenant vacates a location and then transfers to a nearby one.
2. Based on the number of occupied and open locations, the temperature, and the quantity of Frenkel defects, a calculation is made. 
3. Frenkel defects are also known as dislocation Defects since they result from ion displacement. 
4. The Frenkel Defects are caused by particle irradiation.
5. The Frenkel Defects do not confer crystal density or electrical neutrality.
6. The Frenkel Defects do not involve any modification of the chemical characteristics.
7. When an ion or atom takes up an empty space in a crystal lattice, a Frenkel defect develops.