The key difference between Schottky defect and Frenkel defect is that Schottky defect reduces the density of a crystal whereas Frenkel defect does not affect the density of a crystal. Apart from the above key difference, another important difference between Schottky defect and Frenkel defect is that the Schottky defect causes a reduction of the mass of the crystal while Frenkel defect does not affect the mass of the crystal.
The term crystal lattice describes the symmetrical arrangement of the atoms of a crystal. The Schottky defect and Frenkel defect are two forms of point defects that occur in a crystal lattice. A point defect is a vacant point that creates due to the loss of an atom from the crystal lattice. These defects cause irregularity of crystal lattices.
CONTENTS
1. Overview and Key Difference
2. What is Schottky Defect
3. What is Frenkel Defect
4. Side by Side Comparison – Schottky Defect vs Frenkel Defect in Tabular Form
5. Summary
What is Schottky Defect?
Schottky defect is a form of point defect that forms due to the loss of an atom in stoichiometric units of the crystal lattice. This point defect got its name after the scientist Walter H. Schottky. We can observe this defect in either ionic or nonionic crystals. This defect arises when a building block leaves the crystal lattice.
Figure 01: Schottky Defect in NaCl
Although the lattice loses an atom, it does not affect the charge balance of the lattice because the atoms leave a stoichiometric unit of the lattice. A stoichiometric unit contains oppositely charged atoms in equal ratios.
When this defect occurs, it reduces the density of crystal lattice. This form of point defects is common in ionic compounds. When it occurs in nonionic crystals, we call it a vacancy defect. Most of the times, this defect occurs in crystal lattices having atoms with nearly equal sizes. Ex: NaCl lattice, KBr lattice, etc.
What is Frenkel Defect?
Frenkel defect is a form of point defect in which the defect occurs due to the loss of an atom or small ion from the crystal lattice. This loss creates a vacant point in the lattice. Synonyms for this defect are Frenkel disorder and Frenkel pair. The defect got its name after the scientist Yakov Frenkel.
If a small ion leaves the crystal lattice, it is a cation (a positively charged ion). This ion occupies a location nearby the vacant point. Therefore, this defect does not affect the density of the crystal lattice. That is because the atom or ions does not completely leave the lattice. This form of point defects is common in ionic lattices. Unlike in Schottky defect, this defect occurs in lattices with atoms or ions having different sizes.
What is the Difference Between Schottky Defect and Frenkel Defect?
Schottky defect is a form of point defect that forms due to the loss of an atom in stoichiometric units of the crystal lattice. Frenkel defect is a form of point defect in which the defect occurs due to the loss of an atom or small ion from the crystal lattice. The Schottky defect reduces the density of the crystal lattice while the Frenkel defect does not affect the density of the crystal lattice.
Summary – Schottky Defect vs Frenkel Defect
Point defects are defects in crystal lattices that occurs due to the loss of atoms or ions from the lattice and thus, forming a vacant point. Schottky defect and Frenkel defect are two forms of point defects. The difference between Schottky defect and Frenkel defect is that Schottky defect reduces the density of a crystal whereas Frenkel defect does not affect the density of a crystal.
Reference:
1. “Schottky Defect.” Wikipedia, Wikimedia Foundation, 12 May 2018. Available here
2. “Crystal Defects – Point Defects.” Conductors and Insulators. Available here
Image Courtesy:
1.’NaCl – Schottky defect’By VladVD – Own work, (CC BY-SA 3.0) via Commons Wikimedia