Difference Between Schottky Defect And Frenkel Defect

What Is Schottky Defect?

A Schottky defect is a type of point defect in a crystal lattice named after a German physicist Walter H. Schottky who discovered it. In ionic crystals, this type of point defect forms when oppositely charged ions leave their corresponding lattice sites, creating a pair of vacancy defects. These vacancies are formed in Stoichiometric units, to maintain an overall neutral charge in the crystal. The surrounding atoms then move to occupy these vacancies, causing new vacancies to form. Usually, these defects will lead to a decrease in the density of the crystal or metal.  Typically, when the defect is formed in non-ionic crystal it is referred to as lattice vacancy defect.

Schottky defect is found in highly ionic compounds or highly coordinated compounds. The compound lattice has (equal) or small difference in sizes between the anion and cations. Common for example:

• Sodium Chloride (NaCl)
• Potassium Chloride (KCl)
• Potassium Bromide (KBr)
• Silver Bromide (AgBr)
• Cerium Dioxide (CeO₂)
• Thorium Dioxide (ThO₂)
• Caesium Chloride (CsCl)

What You Need To Know About Schottky Defect

• Schottky defect is a type of point defect that occurs due to loss of atoms from a crystalline lattice in stoichiometric units. A stoichiometric unit contains oppositely charged atoms in equal ratios.
• It occurs in ionic crystals where difference in size between cation and anion is small.
• The atoms permanently leave the crystal.
• The number of atoms reduces from the crystal for each Schottky defect.
• Schottky defect results to change in density of the crystal because the volume remains the same while mass is decreased because ions or atoms have left the crystal and created the vacancies.
• Schottky defect occurs in ions and atoms of the same size.
• Schottky defect results to change in chemical properties of the compound.
• In Schottky defect, both cation and anion leave the solid crystal.
• One Schottky defect leads to the formation of two vacancies.
• Schottky defect is found in highly ionic compounds having cations and anions of same sizes e.g Sodium Chloride (NaCl), Potassium Chloride (KCl), Potassium Bromide (KBr), Silver Bromide (AgBr), Cerium Dioxide (CeO₂) and Thorium Dioxide (ThO₂).

What Is Frenkel Defect?

A Frenkel defect also referred to as dislocation defect, is a type of point defect in crystalline solids named after Yakov Frenkel, a Russian physicists who discovered it while engaging in a research of condensed state. The defect forms when an atom or smaller ion leaves its place in the lattice, creating a vacancy and becomes an interstitial by lodging in a nearby location. This defect is only possible if the cations are smaller in size when compared to the anions.

Frenkel defect is common in a crystal with low coordination number or in ionic solids where the smaller ion (usually the cation) is dislocated, for example:

• Zinc Sulfide (ZnS)
• Silver Chloride (AgCl)
• Silver Bromide (AgBr).

What You Need To Know About Frenkel Defect

• Frenkel defect is a type of point defect occurs due to loss of one atom or a small ion.
• It occurs in those ionic crystals where size of anion is quite large as compared to that of the cation.
• In Frenkel defect, atoms leave the original lattice site and occupy interstitial position. Therefore, atoms reside within the solid crystal.
• The number of atoms present in the crystal before and after Frenkel defect remains same.
• Frenkel defect has no effect in the density because the ions or atoms are just being displaced. Therefore, the mass remains the same and the density is unchanged.
• Frenkel defect occurs in ions and atoms of different sizes.
• Frenkel defect does not result in changes in the chemical properties due to the fact that the crystalline structure remains balanced because the atoms are only displaced.
• In Frenkel defect, only the smaller ion (cation) leaves its original lattice site where the anion remains in original lattice sites.
• One Frenkel defect creates one vacancy and one self-interstitial defect.
• Frenkel defect is common in a crystal with low coordination number e.g Zinc Sulfide (ZnS), Silver Chloride (AgCl) and Silver Bromide (AgBr).

Difference Between Schottky Defect And Frenkel Defect In Tabular Form