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Question
Explain the following term with suitable examples:
Frenkel defect
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Solution
This defect arises when an ion (generally a cation) leaves its lattice site and occupies an interstitial site.
The void or empty space between the lattice points is known as an interstitial site. Fig. depicts a Frenkel flaw. It is evident from the image that instead of having its own proper location in the lattice, one of the A+ ions occupies a spot in the interstitial space. As seen in the illustration, this results in a hole being made in the lattice. Because the number of positive ions equals the number of negative ions, the crystal is nonetheless neutral despite this defect, maintaining the compound’s stoichiometry and electrical neutrality.
Frenkel flaws do not impact the crystal’s density. They conduct electricity in crystals and cause diffusion in solids. The presence of Ag+ ions in the interstitial region of AgBr crystals creates photographic images when exposed to light. Frenkel flaws raise the dielectric constant of crystals. Frenkel flaws cause charges to move closer within the crystal.
Frenkel defects are common in silver halides, e.g., AgCl, AgBr and Agl. They are also found in ZnS crystals.
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RELATED QUESTIONS
Give reasons : In stoichiometric defects, NaCl exhibits Schottky defect and not Frenkel defect.
What type of defect is shown by NaCl in
stoichiometric defects, and
non-stoichiometric defects?
Defect shown by non-ionic solids is ____________.
Defects in solids can be studied using
Point defect is also known as ____________.
Frenkel defects are not found in alkali metal halides because ____________.
Type of stoichiometric defect shown by ZnS is ____________.
Type of stoichiometric defect shown by AgBr is ____________.
The following diagram shows:
Schottky defect defines imperfection in the lattice structure of ____________.
Assertion: No compound has both Schottky and Frenkel defects.
Reason: Both defects change the density of the solid.
Schottky defect is observed in crystals when ______.
Match the defects given in Column I with the statements in given Column II.
| Column I | Column II |
| (i) Simple vacancy defect | (a) shown by non-ionic solids and increases density of the solid. |
| (ii) Simple interstitial defect | (b) shown by ionic solids and decreases density of the solid. |
| (iii) Frenkel defect | (c) shown by non ionic solids and density of the solid decreases. |
| (iv) Schottky defect | (d) shown by ionic solids and density of the solid remains the same. |
Given below are two statements, one is labelled as Assertion (A) and the other is labelled as Reason (R):
Assertion: In any ionic solid (MX) with Schottky defects, the number of positive and negative ions are same.
Reason: Equal number of cation and anion vacancies are present.
Given below are two statements:
Statements I: Frenkel defects are vacancy as well as interstitial defects.
Statements II: Frenkel defect leads of colour in ionic solids due to the presence of F-centers.
Choose the most appropriate answer for the statements from the options given below:
Which type of ‘defect’ has the presence of cations in the interstitial sites?
