Frenkel Defect

In crystalline materials, a Frankel defect is a form of point defect named after its discoverer Yakov Frankel. When an atom or smaller ion (often a cation) departs its lattice position, it creates a vacancy and then becomes an interstitial by settling in a nearby spot. They are generated primarily during particle irradiation in elemental systems because their formation enthalpy is typically much greater than that of other point defects, such as vacancies, and thus their equilibrium concentration according to the Boltzmann distribution is less than the detection limit. This defect can also be produced spontaneously in ionic crystals, which typically have a low coordination number or a large discrepancy in the sizes of the ions.

The Frankel defect has no effect on the crystal’s density or stability. Although the defect has a direct effect on the ion’s movement, the volume and density of the solid-state structure remain unchanged. In densely packed formations, interstitial atoms cause strains that cause the lattice to expand. This expansion outweighs the shrinkage of the lattice caused by the vacancy.

Frenkel Defect Formation-

The Frankel flaw can be generated in a variety of ways. The following are the mechanisms by which the Frankel defect is formed: A cation has a tendency to leave its original lattice site and migrate to another interstitial site, depending on its size and the amount of available space. Thus, a void will be generated in the cation’s initial space, which will be used as an interstitial space. This cation that is present between the interstitial space prefers to occupy a location with low repulsion, which allows it to occupy the interstitial space.

• A cation transitions from its own lattice side to the interstitial state
• In the lattice, a vacancy is generated
• The uprooted cation seeks refuge among the other cations and anions in a nearby site

In solid-state systems, defects are common, as the locations of molecules or atoms are specified by the unit cell characteristics in crystals at repeated set distances. Frankel flaws are created mostly through particle irradiation. The majority of the time, a crystal structure is imprecise and vulnerable to change. The enthalpy during the time of creation is greater than at any other point in particle irradiation, and so the equilibrium does not approach the detection limit. The Frankel defect can also emerge spontaneously in systems containing a displaced cation (smaller ion).

Imperfections in Solid Crystals-

One of the most distinguishing properties of crystals over amorphous substances is the precise alignment of ions. However, no material is precisely aligned, and hence flaws called lattice faults are detected.

The term “deficit” refers to flaws or imperfections. Additionally, solid crystals exhibit a variety of flaws that we examine in solid-state chemistry. Certain crystal units may have one or more atoms fewer than other ideal crystal units. These flaws in crystals are referred to as crystal faults. In other terms, crystallographic defects are discontinuities in the regular patterns found in crystalline substances. Crystallographic defects come in a variety of shapes and sizes, including point defects, line defects, and planar defects. Frankel faults are discrete flaws.

The Frenkel Defect’s Cause-

When anions have a substantially greater ionic compound size than cations, the Frenkel Defect develops. Ions occupy an interstitial position in the lattice due to their size disparity. In nature, ionic crystals with Frankel flaws also remain neutral. As long as the ratio of cations to anions remains constant. Thus, those ionic solids with considerable size variations between the cation and anion exhibit Frankel flaws.

The Frankel defect has no effect on the crystal’s density, mass, or volume because ion movement occurs within the crystal. Thus, even with a Frenkel defect, the ionic crystal’s density, mass, and volume remain constant.

Frenkel Defect Characteristics

The Frankel Flaw is a one-of-a-kind defect in which the crystal remains neutral and the proportion of cations and anions remains constant. Cations are smaller than anions in the Frenkel Defect. Because cations and anions have different sizes, the smaller atoms occupy the interstitial spaces.

• Frenkel Defect lattices are rather open
• The Frenkel Defect arises when cations are smaller in size than anions
• In the Frenkel Defect, a solid-state has a low coordination number
• The Frenkel Defect has no effect on a substance’s chemical characteristics
• Because the Frenkel Defect has no effect on the structure’s density, it preserves the solid’s mass and volume
• When conducting the Frenkel Defect, substances preserve their electrical neutrality

Conclusion- 

The Frankel defect results in an ion displacement. This defect is also referred to as a dislocation defect because the smaller ion, the cation, is displaced from its original location and placed in an interstitial location. While the density of the compounds remains constant, they have low coordination numbers and a significant disparity in the size of anions and cations.